BOOK OF ABSTRACTSfama.iff.csic.es/con/SAMS-2010/SAMS-files/Book_of...Rather unexpected new information on the electron phonon coupling comes from Inelastic Helium Atom Scattering (IHAS)

INTERNATIONAL WORKSHOP ON SCATTERING OF ATOMS AND MOLECULES

FROM SURFACES

The Weizmann Institute of Science Rehovot, Israel

October 24 – 28 (2010)

BOOK OF ABSTRACTS

http://www.iff.csic.es/fama/con/SAMS-2010/index.html

1st International Workshop on Scattering of Atoms and Molecules from Surfaces – SAMS-2010

- 2 -


- 3 -

Welcome to the 1st International Workshop on Scattering of Atoms and Molecules from Surfaces, SAMS-2010. The purpose of the Workshop is to bring together scientists working in the general field of atom/molecule surface scattering. Participants include a balanced mix of experimentalists and theorists. Discussions will revolve around recent advances in both experiment and theory, stressing the unsolved and challenging problems which will be faced in the future. The meeting will bring together dynamicists and ab-initio chemistry theorists who will be confronted with the most recent experimental advances, hopefully creating full synergy between all three communities. Eli Pollak The Weizmann Institute of Science


- 4 -


- 5 -

SPONSORS


- 6 -


- 7 -

LIST OF INVITED TALKS Alexandrowicz: A Magnetically Focused Molecular Beam of Spin Selected Ortho-Water

Allison: Quantum Processes in the Scattering of He and Ne Atoms from Adsorbates

Averbukh: Field-Free Molecular Alignment: Prospects for Laser Control of the Scattering Processes

Benedek: Unveiling Mode-Selected Electron-Phonon Interaction in Metal Films by Helium Atom Scattering

Ellis: The Use of Transition State Theory to Interpret Quasi-Elastic Helium Atom Scattering Measurements of Surface Dynamics

Farías: Probing DFT Based 6D Potential Energy Surfaces with H2 Diffraction Experiments

Gerber: Atmospheric Molecular Reactions at Ice and Water Particles

Harrison: He–Atom Scattering from Surfaces: Calculating the Potential Energy Surface from First Principles

Hinch: Adsorbate Diffusion by Hopping between non Bravais Lattice Sites: CpH/Cu(111).

Holst: He-Scattering from SiO2 Surfaces

Kolodney: Velocity Correlated Multifragmentation in Molecule-Surface Impact

Kondo: Molecular Beam Scattering from Solid Surfaces: The Effects on the Scattering of Molecular Anisotropy and Surface Electronic States

Lemoine: Quantum Studies of the Interaction of Hydrogen Atoms with Graphite and Silver Surfaces

Manson: Theory of Direct Scattering, Trapping and Desorption in Atom-Surface Collisions

Martínez-Casado: He–Atom Scattering from Surfaces: Calculating Diffracting Peak Intensities from First Principles

Minton: Scattering Dynamics of Hyperthermal Oxygen Atoms on Ionic Liquid Surfaces: [emim][NTf2] and [C12mim][NTf2]

Miret-Artés: Stochastic Classical Theory for Atom-Surface Scattering

Moix: Energy-Loss Rainbows and Diffraction in Heavy Atom Surface Scattering

Peskin: Bias-Controlled Mode-Selective Vibrational Excitations in Molecular Junctions

Poirier: Quantum Dynamics of Hydrogen Interacting Exohedrally with Single-Walled Carbon Nanotubes


- 8 -

Saalfrank: Open-System Density Matrix Theory for Surface Science Problems

Sibener: Dynamics of Molecular and Polymeric Interfaces Probed with Atomic Beam Scattering and SPM Imaging

Toennies: The Anatomy of the Electron-Phonon Coupling in Thin Lead Films from Helium Atom Scattering

Tully: Vibrational Energy Flow at Metal Surfaces: The Role of Electronic Excitations

Wöll: Chemistry on Oxide Surfaces Revisited with He-Atom Scattering


- 9 -

LIST OF CONTRIBUTED TALKS Avidor: Highly Ordered Water Structures on an Oxygen Precovered Ruthenium Surface

Khodorkovsky: Classical Theory of Rotational Rainbow Scattering from Uncorrugated Surfaces

Kole: A Two Dimensional Approach for Measuring Surface Phonons using Helium Spin Echo

Oh: Angular Intensity Distribution of N2 and CO Scattered from Graphite Surface

Sanz: Multifaceted Dynamical Approach to Adsorption in Surfaces

Shimshovitz: Gaussian Flexibility with Fourier Accuracy: Thinking Inside the Box

Zamstein: Bohmian Mechanics with Complex Action: Application to Nonadiabatic Transitions


- 10 -


- 11 -

CONFERENCE PROGRAM

Wednesday, October 27 Tuesday, October 26 Monday, October 25

He Scattering II

(Miret-Artés)

Hydrogen Dynamics

(Manson)

Electronic Processes at Surfaces

(Pollak)

9:00 – 9:35 Wöll 8:45 – 9:20 Ellis 9:00 – 9:35 Toennies

9:35 – 10:10 Harrison 9:20 – 9:55 Farías 9:35 – 10:10 Tully

10:10 – 10:45 Martínez-Casado 9:55 – 10:30 Lemoine 10:10 – 10:45 Kondo

10:45 – 11:15 Coffee 10:30 – 10:50 Coffee 10:45 – 11:15 Coffee

Interfaces

(Asscher)

Theory

(Tully)

Particle Surface Scattering I

(Sibener)

11:15 – 11:50 Gerber 10:50 – 11:25 Saalfrank 11:15 – 11:50 Manson

11:50 – 12:25 Kolodney 11:25 – 12:00 Miret-Artés 11:50 – 12:25 Averbukh

12:25 – 13:00 Poirier 12:00 – 12:30 Light Lunch 12:25 – 13:00 Minton

13:00 – 14:30 Lunch 12:30 – 19:00 Excursion to Jerusalem 13:00 – 14:30 Lunch

Surfaces and Larger Molecules

(Tannor)

He Scattering I

(Kronik)

14:30 – 15:05 Alexandrowicz 14:30 – 15:05 Benedek

15:05 – 15:40 Hinch 15:05 – 15:40 Holst

15:40 – 16:10 Coffee 15:40 – 16:10 Coffee

Dynamics

(Toennies)

Vibrational Coupling

(Sanz)

16:10 – 16:45 Moix 16:10 – 16:45 Allison

16:45 – 17:20 Sibener 16:45 – 17:20 Peskin

17:20 – 17:30 Pollak

Concluding Remarks

18:30 – 19:30 Dinner

19:00 – 20:00 Dinner 19:00 – 21:00 Dinner in Jerusalem Contributed Talks

(Alexandrowicz)

19:30 – 19:45 Oh

19:45 – 20:00 Sanz

20:00 – 20:15 Khodorkovsky

20:15 – 20:30 Kole

20:30 – 20:45 Avidor

20:45 – 21:00 Zamstein

21:00 Return to Rehovoth 21:00 – 21:15 Shimshovitz


- 12 -


- 13 -

INVITED TALKS

ABSTRACTS


- 14 -


- 15 -

THE ANATOMY OF THE ELECTRON-PHONON COUPLING IN THIN LEAD FILMS FROM HELIUM ATOM SCATTERING

J. P. Toennies

Max Planck Institute for Dynamics and Self-Organization, Bunsenstraße 10, 37073 Göttingen, Germany

The coupling between the electrons and phonons of a metal is of fundamental importance for understanding many basic transport processes, including heat conductivity and electrical conductivity. The electron phonon coupling constant is a basic ingredient in the Bardeen, Cooper, Schrieffer theory of superconductivity. The coupling between the electrons and phonons of a metal also come into play whenever a solid is exposed to excitations from the outside, such as in photoemission, inelastic electron scattering as in tunnelling spectroscopies or at the surface when it is exposed to gas phase collisions. Rather unexpected new information on the electron phonon coupling comes from Inelastic Helium Atom Scattering (IHAS) from thin lead films with between 3-8 monolayers [1]. The time-of-flight spectra reveal an unusually large number of inelastic peaks corresponding to more than ½ of the total number of the expected 2 N modes active in the planar scattering geometry. Sophisticated density function (DFT) calculations have been employed to explore the electron charge density oscillations in response to the phonon induced atomic displacements [2]. Previously similar calculations for the Cu(111) surface [3] revealed that the electron density distributions throughout the surface region are strongly coupled to the surface phonons. These results made it possible to explain the observed excitation of subsurface phonons by assuming that they are excited via the charge distortion resulting from the He atom impact and not by the conventional mechanism of impulsive collisions with the surface atoms. Consistent with the unusually large electron-phonon coupling constant in lead this effect is much larger in the lead films and explains the excitation of the large number of subsurface phonons. A preliminary theoretical analysis suggests that the inelastic intensities are closely related to the mode specific electron-phonon coupling constants. Thus the DFT calculations provide the “anatomy” of the electron-phonon coupling constant corresponding to each of the measured electron-phonon coupling constants.

[1] J. Braun, P. Ruggerone, Ge. Zhang, J. P. Toennies and G. B. Benedek, Phys. Rev. B 79, 205423 (2009).

[2] V. Chis, B. Hellsing, G. Benedek, M. Bernasconi, E. V. Chulkov and J. P. Toennies, Phys. Rev. Lett. 101, 206102 (2008).

[3] I. Yu. Sklyadneva, E. V. Chulkov, P. M. Echenique, R. Heid, K.-P. Bohnen, G. Benedek and J. P. Toennies (in preparation).


- 16 -

VIBRATIONAL ENERGY FLOW AT METAL SURFACES:

THE ROLE OF ELECTRONIC EXCITATIONS

J. C. Tully

Department of Chemistry, Yale University, New Haven, CT (USA)

Breakdown of the adiabatic (Born-Oppenheimer) approximation is the rule rather than the exception for molecular dynamics at metal surfaces. Electron-hole pair transitions, charge transfer and hot-electron-induced motion can be dominant pathways for vibrational energy flow and can drastically alter chemical reaction pathways. Recent experiments have demonstrated that molecular vibrational energy and reaction exothermicity can produce highly excited electrons, even resulting in electron emission. This talk will present progress toward a unified picture of nonadiabatic dynamics at metal surfaces, with application to multi-quantum vibrational-to-electronic energy transfer in the scattering of nitric oxide from a gold surface.


- 17 -

MOLECULAR BEAM SCATTERING FROM SOLID SURFACES:

THE EFFECTS ON THE SCATTERING OF MOLECULAR ANISOTROPY AND SURFACE ELECTRONIC STATES

T. Kondo

Institute of Frontier Science, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8573, Japan

RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, 351-0198, Japan

The gas-surface collision is the initial step of all of the chemical reactions on a surface. During collision processes, the kinetic energy of reactant gas molecules is dissipated into such channels as phonon creation and/or electronic excitation in solid, internal mode excitation of gas molecules, and so on. The energy dissipative inelastic collision process depends on the energy state of the incoming molecule, the surface temperature and the potential energy surface of the molecule interacting with the surface. We have investigated the gas-surface scatterings for wide variety of molecules such as CO, N2, H2O, O2, CH4 and C2H6 as well as He, Ne and Ar from LiF(001), Pt(111), graphene/Pt(111), graphite(0001) and their electronically modified surfaces. Here, the effects of the molecular anisotropy and the surface electronic states on the gas-surface scattering are discussed in detail. The effect of the molecular anisotropy can be clearly observed in the rainbow feature of the scattering. On the LiF(001) surface, most of the molecules show rainbow scattering feature when they scattered from the plane along the [001] direction due to the large corrugation amplitude of the interaction potential. With an increase in the extent of the molecular anisotropy, the rainbow feature is clearly smeared out. The detail of its origin will be discussed with the calculated results by the simple classical binary collision model. The effect of the local electronic modification of the surface on the scattering can be clearly observed for the He and Ar scatterings from bare and defect induced graphite surfaces. The modulated electronic states of graphite around the defect causes the large scattering cross-section for the He diffuse scattering (113 nm2) and large energy loss of Ar by the collision due to the local breaking of the π conjugated system of graphite. The details of its origin will be discussed with the results of scanning tunneling microscopy and spectroscopy.


- 18 -

THEORY OF DIRECT SCATTERING, TRAPPING AND DESORPTION

IN ATOM-SURFACE COLLISIONS

J. R. Manson and G. Fan

Clemson University, Clemson, SC (USA)

When gas atoms or molecules collide with clean and ordered surfaces, under many circumstances the energy-resolved scattering spectra exhibit two clearly distinct features due to direct scattering and to trapping in the physisorption well with subsequent desorption. This situation was first described by James Clerk Maxwell in a paper which invoked the simple assumption that when an impinging gas beam is scattered from a surface it can be divided into a part that reflects directly with little change in state and another part that adsorbs and accommodates completely and then desorbs with an equilibrium distribution [1]. This work is a scattering theory using classical mechanics for the collision process that describes both direct scattering and trapping-desorption of the incident beam. The initially trapped particles can be followed as they continue to make further interactions with the surface until they are all eventually promoted back into the positive energy continuum and leave the surface region. Consequently, this theory provides a test of the Maxwell assumption and determines the conditions under which it is valid. Additionally, the theory gives quantitative explanations of important experimental measurements [2] for scattering of Ar atoms by a self assembled layer of 1-decanethiol on Au(111) which exhibit both a direct scattering contribution and a trapping-desorption fraction in the energy-resolved spectra [3]. [1] J. C. Maxwell, Phil. Trans. Royal Soc. Lond. 170, 231 (1879).

[2] K. D. Gibson, N. Isa and S. J. Sibener, J. Chem. Phys. 119, 13083 (2003).

[3] Guoqing Fan and J. R. Manson, Phys. Rev. Lett. 101, 063202 (2008);

Phys. Rev. B 79, 045424 (2009).


- 19 -

FIELD-FREE MOLECULAR ALIGNMENT:

PROSPECTS FOR LASER CONTROL OF THE SCATTERING PROCESSES

E. Gershnabel, Yu. Khodorkovsky, J. Floss and I. Sh. Averbukh Department of Chemical Physics, The Weizmann Institute of Science, Rehovot, Israel

Recent years witness a tremendous progress in developing new methods for controlling molecular rotational motion with the help of ultrashort laser pulses. Field-free molecular alignment, laser-induced unidirectional molecular rotation, and even full 3D control over molecular orientation in space are only few examples to mention. We will overview recent developments in the field, and will discuss the prospects of using this newly emerging toolbox for controlling molecular scattering of different kinds, including surface scattering.


- 20 -

SCATTERING DYNAMICS OF HYPERTHERMAL OXYGEN ATOMS ON

IONIC LIQUID SURFACES: [emim][NTf2] AND [C12mim][NTf2]

B. Wua, J. Zhanga, T. K. Mintona, K. G. McKendrickb, J. M. Slatteryc, S. Yockeld and G. C. Schatzd

aDepartment of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA

bSchool of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK

cDepartment of Chemistry, University of York, Heslington, York YO10 5DD, UK

dDepartment of Chemistry, Northwestern University, Evanston, IL 60208-3113, USA

Collisions of hyperthermal oxygen atoms, with an average laboratory-frame translational energy of 520 kJ mol-1, on continuously refreshed ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([emim][NTf2]) and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C12mim][NTf2]), were studied with the use of a beam-surface scattering technique. Time-of-flight and angular distributions of inelastically scattered O and reactively scattered OH and H2O were collected for various angles of incidence with the use of a rotatable mass spectrometer detector. For both O and OH, two distinct scattering processes were identified, which can be empirically categorized as thermal and non-thermal. Non-thermal scattering is more probable for both O and OH products. The observation of OH confirms that at least some reactive sites, presumably alkyl groups, must be exposed at the surface. The ionic liquid with the longer alkyl chain, [C12mim][NTf2], is substantially more reactive than the liquid with the shorter alkyl chain, [emim][NTf2], and proportionately much more so than would be predicted simply from stoichiometry based on the number of abstractable hydrogen atoms. Molecular dynamics models of these surfaces shed light on this change in reactivity. The scattering behavior of O is distinctly different from that of OH. However, no such differences between inelastic and reactive scattering dynamics have been seen in previous work on pure hydrocarbon liquids, in particular the benchmark, partially branched hydrocarbon, squalane (C30H62). The comparison between inelastic and reactive scattering dynamics indicates that inelastic scattering from the ionic liquid surfaces takes place predominantly at non-reactive sites that are effectively stiffer than the reactive alkyl chains, with a higher proportion of collisions sampling such sites for [emim][NTf2] than for [C12mim][NTf2].


- 21 -

UNVEILING MODE-SELECTED ELECTRON-PHONON INTERACTION

IN METAL FILMS BY HELIUM ATOM SCATTERING

G. Benedek* Donostia International Physics Centre (DIPC), Donostia/San Sebastian, Spain

Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Milano, Italy

The quasi two-dimensional electron gas of a metal film can transmit to the surface any tiny mechanical disturbance occurring in the depth, thus allowing the gentlest of all surface probes, helium atoms, to perceive the vibrations of the deepest atoms via the induced surface-charge density oscillations. Moreover this kind of quantum sonar driven by electron density waves conveys direct information on the electron-phonon coupling of individual phonons of selected energy and momentum. A density functional perturbation theory (DFPT) and a helium atom scattering study of the phonon dispersion curves in lead films of up to 7 monolayers on Cu(111) show that: (a) the electron-phonon interaction is responsible for the coupling of He atoms to underground phonon modes; and (b) the inelastic HAS intensity from a given phonon mode is proportional to its electron-phonon coupling. The direct determination of mode-selected electron-phonon coupling constants is believed to have great relevance in the study of thin-film superconductivity. *Work performed together with: I. Yu. Sklyadneva, E. V. Chulkov and P. M. Echenique (DIPC and

UPV, Donostia/San Sebastián, Spain); R. Heid K.-P. Bohnen (Forschungscentrum Karslruhe,

Germany); J. P. Toennies (MPI-DS, Goettingen, Germany).


- 22 -

HE-SCATTERING FROM SIO2 SURFACES

B. Holst University of Bergen, Department of Physics and Technology, Allegaten 55, 5007 Bergen, Norway

More than 90% of the earths crust is made of silicates. SiO2 in the form of quartz (sand) is the most common mineral in the continental crust. Quartz and the amorphous form of SiO2, Silica glass, have numerous industrial applications. Despite the fact that quartz is one of the most common minerals on earth and despite the vast range of applications, so far little fundamental work on the structure and dynamical properties of SiO2 surfaces has been done. Presumably because the properties of SiO2 surfaces makes difficult to investigate them with many surface science techniques (SiO2 is an insulator and the outermost layer consists solely of oxide atoms) Here we present new results which for the first time reveal the surface structure of the α-quartz (0001) surface. The surface was investigated using Helium Atom Scattering (HAS) and Atomic Force Microscopy. We show that α-quartz (0001) forms a superlattice structure with a periodicity in the 5 nanometre range. AFM measurements clearly show that the superlattice structure consists of three domains rotated by 120° relative to each other. In HAS the corresponding hexagonal satellite peak pattern can be observed around the main peaks in the diffraction pattern. The satellite peak pattern is rotated by several degrees with respect to the bulk high symmetry directions, indicating a rotation of the superlattice structure with respect to the bulk. In a further experimental step we investigated the dynamical properties of the α-quartz (0001) by identifying surface phonons in the low energy range. Experiments have been performed also on hydrogen passivated quartz. Finally we show first helium atom scattering measurements attempting to reveal information about the surface structure of Silica glass.


- 23 -

QUANTUM PROCESSES IN THE SCATTERING OF

HE AND NE ATOMS FROM ADSORBATES

W. Allison Surface Physics Group, Cavendish Laboratory, University of Cambridge CB3 0HE, UK

At thermal energies, light atoms exhibit behaviour that spans both the quantum and classical worlds. Experience in atom-surface scattering suggests that He atoms are essentially quantum since diffraction, with no energy loss, is the dominant process, while heavier Ne atoms, behave more classically and scatter inelastically. In this talk I will present recent examples from experiment where the simple expectations of quantum and classical behaviour are confounded. Specifically, when Ne scatters from an alkali metal film, the degree of inelasticity in the scattering does not follow the classical expectation based on the mass ratio of projectile and target. We observe that when the target is a light alkali metal, such as Li, a high degree of elastic scattering is observed, whereas a heavier target, like Na, results in predominantly inelastic scattering. In the case of Li, the degree of inelasticity is profoundly affected by the presence, or absence, of in-plane bonds within the adsorbate layer [1]. Recent developments in the technique of He scattering have allowed details of microscopic, quantum processes in the behaviour of adsorbates to be studied [2]. The atom, spin-echo method provides information with a unique combination of time- and distance-scales and a variety of adsorbates have been studied. By comparing the behavior of atomic and molecularly bonded systems, new insights into the origin of molecular-scale friction and the connection between friction and the corrugation of the landscape have emerged [3]. In the case of the lightest adsorbates, H and D, quantum effects in the adsorbate dynamics have also been revealed [4]. Finally, I discuss recent experimental evidence for quantum effects that have been predicted [5] to occur in the quasi-elastic lineshape. These effects correspond to the minute effect of recoil in the adsorbate as it responds to interactions with the incident helium atom. [1] C. Huang, G. Fratesi, D. A. MacLaren, W. Luo, G. P. Brivio and W. Allison, Phys. Rev. B 82, 081413 (2010); A. C. Levi, C. Huang, W. Allison and D. A. MacLaren, J. Phys.: Condens. Matter 21, 225009 (2009).

[2] A. P. Jardine, G. Alexandrowicz, H. Hedgeland, W. Allison and J. Ellis, Phys. Chem. Chem. Phys. 11, 3355 (2009).

[3] H. Hedgeland, P. Fouquet, A. P. Jardine, G. Alexandrowicz, W. Allison and J. Ellis, Nature Physics 5, 561 (2009).

[4] A. P. Jardine, E. Y. M. Lee, D. J. Ward, G. Alexandrowicz, H. Hedgeland, W. Allison, J. Ellis and E. Pollak, Phys. Rev. Lett. (in press, 2010).

[5] R. Martínez-Casado, A. S. Sanz and S. Miret-Artés, J. Chem. Phys. 129, 184704 (2008).


- 24 -

BIAS-CONTROLLED MODE-SELECTIVE VIBRATIONAL EXCITATIONS

IN MOLECULAR JUNCTIONS

R. Volkovicha, U. Peskina, R. Haertleb and M. Thossb aTechnion – Israel Institute of Technology, Haifa, Israel

bFriedrich-Alexander-Universitat Erlangen-Nurnberg, Erlangen, Germany

Single molecule junctions have been the subject of active research during recent years, due to their potential nano technological applications as well as their challenging fundamental characteristics. The coupling of a molecule to two different surfaces of different chemical potentials drives it into a non equilibrium steady state, in which both the energy and the charge on the molecule can be controlled and tuned by the applied bias on the junction. In this work we raise the possibility of bias-controlled, selective excitation of specific molecular vibrational degrees of freedom in the molecular junction scenario. Using model systems we show that for non-symmetric junctions, the competition between different relaxation processes (such as phonon absorption/emission and electron hole pairs creation) at the molecule-electrodes interfaces, is likely to result in bias controlled mode-selective excitations of different internal molecular modes, suggesting a new rout for bias-controlled mode-selective excitation and mode-selective chemistry.


- 25 -

THE USE OF TRANSITION STATE THEORY TO INTERPRET QUASI-ELASTIC HELIUM ATOM SCATTERING MEASUREMENTS OF SURFACE DYNAMICS

J. Ellis Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK

Whilst it is clear that the temperature dependence of rate processes will be dominated by the energy barriers between initial and final states, the absolute value of the rate (as expressed in the pre-exponential value 0ν of a typical activated process TkE Be−= 0νν ) has been the subject of extensive theoretical study [1]. In the context of surface diffusion, however, there has been relatively little successful application of these theories to real systems. One reason for this is that the experimentally determined pre-exponential values are often not accurate enough to permit meaningful comparison with theory. Another reason is that any technique that relies on transport over macroscopic distances will inevitably be affected by the need to jump over steps on the surface. Quasielastic helium atom scattering overcomes both these problems, giving accurate values of the pre-exponential values, and measuring diffusion predominantly over flat terraces [2]. We start by considering how the relatively transparent, but inaccurate, transition state theory relates to accurate versions of rate theory formulated in terms of the adsorbate/surface friction coefficient, and use this understanding to help interpret QHAS data on a number of systems. Firstly we see how the relative density of states (DoS) at the ground and transition states plays an important role in the interpretation of data. In the case of Xe on Pt(111) we show that the observed, quasi-ballistic component of the motion is due to atoms in the excited ‘transition’ state, and that the high population of the transition state arises from the high DoS in the transition state induced by the form of the Xe-Pt(111) potential energy surface, and then we consider how similar arguments can explain the observed absolute rate of diffusion of CO on Cu(001) [3] and C6H6 on Cu(001). In a quantum case (the diffusion of H and D on Pt(111)) we show that, despite very different sets of energetic states [4], H and D diffuse in a remarkably similar way, which indicates that a rate theory, such as quantum transition state theory, that works directly from the adatom–substrate potential energy surface, without detailed consideration of the individual states involved, can be very useful in predicting the diffusion rate. Finally we show that the classical ideas of the effect of friction on the rate of diffusion carry over to the quantum mechanical processes of inter and intra band scattering rates involved in tunneling, and show, with reference to the H/D-Pt(111) system how QHAS data can be used to put limits on the rates of these processes. [1] P. Hänggi, P. Talkner and M. Borkovec, Rev. Mod. Phys. 62, 257 (1990).

[2] A.P. Jardine, H. Hedgeland, G. Alexandrowicz, W. Allison and J. Ellis, Prog. Surf. Sci. 84, 323

(2009).

[3] G. Alexandrowicz, A. P. Jardine, P. Fouquet, S. Dworski, W. Allison and J. Ellis, Phys. Rev.

Lett. 93, 156103 (1994).

[4] S. C. Badescu, P. Salo, T. Ala-Nissila, S. C. Ying, K. Jacobi, Y.Wang, K. Bedurftig and G. Ertl,

Phys. Rev. Lett. 88, 136101 (2002); S. C. Badescu, Ph.D thesis (Brown University, 2003).


- 26 -

PROBING DFT BASED 6D POTENTIAL ENERGY SURFACES

WITH H2 DIFFRACTION EXPERIMENTS

D. Farías Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, 28049 Madrid, Spain

Studies of elementary collision processes of H2 with metal surfaces can provide benchmark tests [1] of theoretical methods that are used to aid the design of new heterogeneous catalysts. Molecular beam and associative desorption experiments have been carried out to understand the main factors that govern H2 dissociation at the surface, while vibrationally inelastic and rotationally inelastic scattering experiments have provided useful information on how certain features of the potential energy surface (PES) control the experimental observations.

A different point of view is provided by diffraction experiments. H2 diffraction from metal surfaces is more complex than He diffraction, since the PES is six-dimensional and the coupling with the dissociative adsorption channels comes into play [2]. Thus, H2 diffraction is a very promising technique to gauge the molecule-surface PES and dynamics. We have recently shown that this is possible by performing H2 diffraction experiments on Pd(111), Pt(111), Ru(0001) and NiAl(110) surfaces at incident energies between about 20 and 160 meV. By comparing the experimental data with six-dimensional quantum dynamics calculations we showed that accurate diffraction patterns can be obtained from state-of-the-art PES based on DFT calculations [3]. In this talk, I will present recent experimental results which might help us to answer some of the following important questions: (1) Can reaction and diffractive scattering of H2 be accurately described using the Born-Oppenheimer approximation [4]?; (2) Which of both PW91 or RPBE functionals provides a better description of H2 diffraction?; (3) Are rotationally inelastic diffraction (RID) peaks more sensitive than elastic diffraction peaks to the quality of the DFT based PES? [1] G. J. Kroes and M. F. Somers, J. Theor. Comput. Chem. 4, 493 (2005). [2] D. Farías and K. H. Rieder, Rep. Prog. Phys. 61, 1575 (1998). [3] D. Farías, C. Díaz, P. Rivière, H. F. Busnengo, P. Nieto, M. F. Somers, G. J.Kroes, A. Salin and F. Martín, Phys. Rev. Lett. 93, 246104 (2004). [4] P. Nieto, E. Pijper, D. Barredo, G. Laurent, R. A. Olsen, E. J. Baerends, G. J. Kroes and D. Farías, Science 312, 86 (2006).


- 27 -

QUANTUM STUDIES OF THE INTERACTION OF HYDROGEN ATOMS

WITH GRAPHITE AND SILVER SURFACES

B. Lepetita, D. Lemoinea, S. Naveb and B. Jacksonc aLaboratoire Collisions Agrégats Réactivité, CNRS-Université Paul Sabatier Toulouse, France

bInstitut des Sciences Moléculaires d’Orsay, CNRS-Université Paris-Sud, France cDepartment of Chemistry, University of Massachusetts, Amherst, USA

In the ITER nuclear fusion reactor project plasma heating is mainly accomplished by the injection of highly energetic neutral atoms (D) obtained from a negative ion source. A promising approach for the development of such a negative ion source is based on cold hydrogen plasma and involves two steps: i) production of vibrationally-excited hydrogen molecules on a surface through the sticking and the recombination of hydrogen atoms ii) followed by the process of dissociative attachment with the slow electrons of the plasma. This creation mechanism relies on a weak adsorption energy of the atoms, like on graphene as a limiting case [cf. J. Chem. Phys. 114, 474 (2001)]. In addition, associative detachment with atomic hydrogen is an important loss mechanism of negative ions in the plasma volume. Thus, a large adsorption energy of the atoms may minimize these losses, e.g. on many metal surfaces. In close collaboration with experiments in Grenoble, France [cf. AIP Conf. Proc. 1097, 74 (2009)] we aim at characterizing surface materials that either trap and retain the atoms (minimization of volume losses) or generate efficiently molecules in a highly-excited vibrational state (which facilitates gains via dissociative electron attachment). It is also useful to determine optimal functioning conditions (plasma temperature, surface temperature …). Graphite has been much studied experimentally and theoretically, specially because it is one laboratory model for interstellar grains on which the formation of molecular hydrogen takes place. Several quantum dynamics studies of the sticking of hydrogen atoms, typically based on electronic structure calculations relying on density functional theory (DFT), are published. Yet, few of them include a sound treatment of the coupling to the bath of phonon modes. We have compared various strategies addressing this latter point. The adsorption of hydrogen atoms is weak on silver surfaces in comparison with most other metal surfaces and one may therefore expect a competition between the creation and loss mechanisms mentioned above. Another motivation for studying silver surfaces is to make up for the absence of theoretical modeling of the recent experiments of Kolovos-Vellianitis and Küppers on the abstraction of D on Ag(100) and Ag(111) by gaseous H atoms [Surf. Sci. 548, 67 (2004)]. To start with we generate the potential energy surfaces for the interaction of a single hydrogen atom by means of DFT calculations. They will be used to compute sticking properties that play a role in both the creation and loss mechanisms.


- 28 -

OPEN-SYSTEM DENSITY MATRIX THEORY FOR SURFACE SCIENCE PROBLEMS

P. Saalfrank

Institut für Chemie, Universität Potsdam, D-14476 Potsdam-Golm, Germany

Molecules or atoms interacting with solid surfaces constitute typical “system-bath” type problems, in which a system (the molecule or atom) interacts with a bath of unobserved degrees of freedom (the surface), leading to energy and phase relaxation. Detailed insight into energy and phase flow during laser pulse-induced processes or scattering events, for example, can be gained by a time-dependent approach. One way to model the quantum dynamics for this kind of problems is by reduced (open-system) density matrix theory, another one by explicit solution of a multi-dimensional, time-dependent Schrödinger equation based on a system-bath Hamiltonian. In the presentation, various flavours of open-system density matrix theory and its numerical realization will be presented. Where possible, the solutions are compared to those obtained from the full, albeit approximate, time-dependent Schrödinger equation. Several examples for dissipative dynamics, all related to surface science will be presented to illustrate the concepts: (i) The selective laser-pulse control of vibrating adsorbates at surfaces, (ii) dissipative, laser-driven electron dynamics near surfaces, and (iii) dissipative molecule-surface scattering.


- 29 -

STOCHASTIC CLASSICAL THEORY FOR ATOM-SURFACE SCATTERING

S. Miret-Artésa, J. Moixb and E. Pollakb

aDepartamento de Física Atómica, Molecular y de Agregados, Instituto de Física Fundamental, CSIC C/ Serrano 123, 28006 Madrid, Spain

bChemical Physics Department, Weizmann Institute of Science,76100 Rehovoth, Israel

The scattering of atoms by surfaces continues to be of both theoretical and experimental interest. Quantum diffraction, which appears even for atoms as heavy as Ar is focusing most of the work in this field. However, many features measured for the scattering of heavy atoms are classical in nature. It is thus of interest to further develop the classical mechanics theory of atom surface scattering. There are a number of major features which any theory should account for. One is the rainbow structure of the angular distribution. For in plane scattering this leads to a typical two peaked distribution whose minimum lies around the specular scattering angle. A second feature is the broadening of the distribution which is due to the interaction of the projectile with the surface and bulk phonons. The third feature has to do with the angular dependence of the energy transfer to the surface [1-5].

In this talk, we review and extend to three dimensions our previous stochastic classical theory on surface rainbow scattering. The stochastic phonon bath is modelled in terms of linear coupling of the phonon modes to the motion of the scattered particle. We take into account the three polarizations of the phonons. Closed formulae are derived for the angular and energy loss distributions. They are readily implemented when assuming that the vertical interaction with the surface is described by a Morse potential. The hard wall limit of the theory is derived and applied to some model corrugated potentials. We find that rainbow structure of the scattered angular distribution reflects the underlying symmetries of the surface. We also distinguish between "normal rainbows" and "super-rainbows". The latter occur when the two eigenvalues of the Hessian of the corrugation function vanish simultaneously.

[1] E. Pollak, S. Sengupta and S. Miret-Artés, J. Chem. Phys. 129, 054107 (2008).

[2] E. Pollak and S. Miret-Artés, J. Chem. Phys. 130, 194710 (2009);

[Erratum, J. Chem. Phys 132, 049901 (2010)].

[3] E. Pollak, J. Moix and S. Miret-Artés, Phys. Rev. B. 80, 165420 (2009);

[Erratum, Phys. Rev. B 81, 039902 (2010)].

[4] J. Moix, E. Pollak and S. Miret-Artes, Phys. Rev. Lett. 104, 116103 (2010).

[5] E. Pollak and S. Miret-Artés, Chem. Phys. (in press, 2010).


- 30 -

CHEMISTRY ON OXIDE SURFACES REVISITED WITH He-ATOM SCATTERING

Ch. Wöll

Institute of Functional Interfaces, Karlsruhe Institute of Technology, Germany

Scattering of thermal energy He atoms is a particularly useful technique for the investigation of hydrogen atoms and other small molecules adsorbed on surfaces in general and on oxides in particular. First, the cross-section of e.g. H atoms adsorbed on an otherwise perfect substrate is fairly large (>10 Å2). This is in pronounced contrast to electron scattering, where the fairly small cross section of H-atoms for electrons makes their detection rather difficult. Second, He atoms are neutral and are thus not affected by charging effects. Third, and possibly most importantly, He atom scattering and neutron scattering are the only diffraction techniques with which the structure of adlayers can be determined without either primary or secondary electrons. This is an important aspect for oxides, where e-h pairs generated by impinging electrons (or photons) can lead to the desorption or chemical modification of adsorbates. The detection of thermal induced desorption is a particular useful method to determine reliable binding energies of small molecules like CO on metal oxide single crystals. In contrast to conventional thermal desorption spectroscopy, TDS, He-TDS allows to separately determine desorption from perfect areas of a surface, which allows to determine reliable benchmark binding energies needed for the validation of theoretical methods. In the talk several examples will be presented for ZnO, TiO2 and Al2O3 substrates. [1] B. Meyer, D. Marx, O. Dulub, U. Diebold, M. Kunat, D. Langenberg and Ch. Wöll, Angew. Chem. Int. Ed. 43, 6642 (2004).

[2] Y. Wang, B. Meyer, X. Yin, M. Kunat, D. Langenberg, F. Traeger, A. Birkner and Ch. Wöll, Phys. Rev. Lett. 95, 266104 (2005).

[3] M. Kunat, B. Meyer, F.Traeger and Ch.Wöll, Phys. Chem. Chem. Phys. 8, 1499 (2006).

[4] Y. Wang, R. Kováčik, B. Meyer, K. Kotsis, D. Stodt, V. Staemmler, H. Qiu, F. Traeger, D. Langenberg, M. Muhler and Ch. Wöll, Angew. Chem. Int. Ed. 46, 5624 (2007).

[5] Ch. Wöll, Prog. Surf. Sci. 82, 55, (2007).

[6] X.-L. Yin, M. Calatayud, H. Qiu, Y. Wang, A. Birkner, C. Minot and Ch. Wöll, ChemPhysChem 9, 2, 253 (2008).


- 31 -

HE–ATOM SCATTERING FROM SURFACES:

CALCULATING THE POTENTIAL ENERGY SURFACE FROM FIRST PRINCIPLES

R. Martínez-Casadoa, G. Malliaa, D. Usvyatb, L. Maschioc,d, S. Casassac,d, M. Schützb and N. M. Harrisona,e

aDepartment of Chemistry, Thomas Young Centre, Imperial College, London SW7 2AZ, UK bUniversity of Regensburg, Institute of Physics and Chemistry, D-93040 Regensburg, Germany

cDepartment of Chemistry IFM, University of Torino, Via P. Giuria 5, 10125 Torino, Italy dNIS Centre of Excellence, Department of Chemistry, Via P. Giuria 5, 10125 Torino, Italy

eSTFC, Daresbury Laboratory, Daresbury, Warrington WA4 4AD, UK

The interpretation of He-atom scattering spectra requires a reliable model of the potential energy surface (PES) for the He-surface interaction. Empirical models of the interaction, whether based on global characteristics of the PES or on pair wise interaction models, inevitably introduce approximations that become difficult to control particularly when the nature of the bonding of the surface is unclear. Predictive first principles calculations provide a reliable basis for discussing surface structure, composition and dynamics but the dominant method for studying crystalline surfaces, density functional theory in the local and semi-local approximations, is inadequate for studying weak interactions. Moller Plessett perturbation theory (MP2) is a post-Hartree-Fock method which provides at least a qualitatively correct description of weak interactions. In this talk we will present data computed with the CRYSCOR package [1] in which a periodic local MP2 approach has been used to compute the PES for He interacting with some common oxides [2]. The functional form of the PES will be compared to that computed using alternative methods and to that resulting from empirical models. The possibility of using this approach to establish a reliable and convenient tool for the interpretation of He-atom scattering spectra will be discussed. [1] M. Halo, S. Casassa, L. Maschio and C. Pisani, Chem. Phys. Lett. 467, 294 (2009).

[2] R. Martínez-Casado, G. Mallia, D. Usvyat, L. Maschio, S. Casassa, M. Schütz and N. M. Harrison, J. Chem. Phys. (accepted for publication, 2010).


- 32 -

HE–ATOM SCATTERING FROM SURFACES:

CALCULATING DIFFRACTING PEAK INTENSITIES FROM FIRST PRINCIPLES

R. Martínez-Casadoa, G. Malliaa, D. Usvyatb, L. Maschioc,d, S. Casassac,d, M. Schützb and N. M. Harrisona,e

aDepartment of Chemistry, Thomas Young Centre, Imperial College, London SW7 2AZ, UK bUniversity of Regensburg, Institute of Physics and Chemistry, D-93040 Regensburg, Germany

cDepartment of Chemistry IFM, University of Torino, Via P. Giuria 5, 10125 Torino, Italy dNIS Centre of Excellence, Department of Chemistry, Via P. Giuria 5, 10125 Torino, Italy

eSTFC, Daresbury Laboratory, Daresbury, Warrington WA4 4AD, UK

The quantitative analysis and correct interpretation of He-atom experiments basically consists of two steps: determining the He-surface interaction potential and using dynamical methods to compute the diffraction intensities. Once the full ab-initio He-surface interaction potential has been calculated [1], the simulation of the He-surface diffraction will be followed by using the Close-Coupling (CC) method [2]. The CC equations come from the time-independent Schrödinger equation for the nuclei after considering the surface periodicity and then integrating over the area of a single surface unit cell. These equations are solved with the appropriate boundary conditions. The square moduli of the outgoing wave amplitudes obtained by solving the CC equations are related to the diffraction probabilities or intensities. The generated intensities correspond to a zero surface temperature and, in order to compare with the experimental intensities, the effects of the thermal vibrations need to be approximated by using a Debye-Waller factor. The utility of the scattering for probing dynamical processes at surfaces is significantly enhanced by this new theoretical description. [1] R. Martínez-Casado, G. Mallia, D. Usvyat, L. Maschio, S. Casassa, M. Schütz and N. M. Harrison, J. Chem. Phys. (accepted for publication, 2010).

[2] A. S. Sanz and S. Miret-Artés, Phys. Rep. 451, 37 (2007).


- 33 -

ATMOSPHERIC MOLECULAR REACTIONS AT ICE AND WATER PARTICLES

R. B. Gerber

Institute of Chemistry, Hebrew University, Jerusalem, 92904 Israel

Department of Chemistry, University of California, Irvine, CA 92697-2025 USA

Atmospheric reactions at water and ice surfaces are studied by Molecular Dynamics simulations, using small H2O clusters as model systems. The core of the approach is the novel use of relatively high-level ab initio potentials directly in the Molecular Dynamics. The most important findings from several applications studied are: (a) The atmospheric processes of interest on macroscopic surfaces are described very well by small water cluster models. (b) In several of the processes, the water molecules play a catalytic role. (c) For several reactions, the mechanism of the catalytic role of water is essentially obtained at the level of one water molecule – “single H2O catalysis”. The processes are studied in all cases with strong links to experiments, and include: The cleavage of N2O4 at water into NO+ and NO3

- ions; the formation of ClNO from N2O4 and HCl, and the photochemistry of peroxides at ice particles. It is suggested that MD simulations for small clusters, using adequate ab initio potentials, are a powerful tool for unravelling mechanisms of chemical reactions at water surfaces.


- 34 -

VELOCITY CORRELATED MULTIFRAGMENTATION

IN MOLECULE-SURFACE IMPACT

E. Kolodney Department of Chemistry, Technion – Israel Institute of Technology, Haifa 32000, Israel

Multifragmentation (MF) phenomena where highly energized complex, finite system simultaneously disintegrates into several of its constituents are important in many fields and are sometimes of a universal nature regarding the general patterns revealed. Once the impact deposited energy exceeds that corresponding to the evaporation regime (sequential emission of elementary sub-units) and approach the total cohesion energy of the system, MF dynamics will start to dominate, eventually reaching complete disintegration of the system into its smallest units (the shattering limit). Recently we have reported [1] that surface impact induced MF of a large molecular system (C60) can be a fully correlated event. By measuring field free kinetic energy distributions (KEDs) of many

(n= 1-12) fragments following collisions of 300-900 eV nC −60C − ions with a gold surface we

have observed the transition from MF with common average energy for all fragments (“during- collision event”) to a one with a common average velocity for all fragments (“post-collision event”) . KEDs for both MF modes were successfully reproduced within a “precursor mediated statistical MF” model using shifted Maxwellian flux distributions .This MF scenario was observed also for 60C − / nickel impact where both KEDs and angular distributions were measured for the outgoing nC − fragments. A novel gradual narrowing effect of the angular distributions was observed and found to be in good agreement with prediction of the precursor model. [1] C. A. Kaplan, A. Bekkerman, B. Tsipinyuk and E. Kolodney, Phys. Rev. B 79, 233405 (2009).


- 35 -

QUANTUM DYNAMICS OF HYDROGEN INTERACTING EXOHEDRALLY

WITH SINGLE-WALLED CARBON NANOTUBES

B. Poiriera and J. McAfeeb aDepartment of Chemistry and Biochemistry, Texas Tech University

bDepartment of Chemistry, University of North Texas, Denton

This work investigates the fundamental dynamical interactions of hydrogen with single-walled carbon nanotubes, addressing possible ramifications for hydrogen storage via the catalytic spillover mechanism. In the first study [1], a single H atom was employed; spin-polarized density functional theory (DFT) calculations were performed for a single hydrogen atom interacting exohedrally with a (5,5) single-walled carbon nanotube (SWNT), and also full 3D quantum dynamics calculations to compute all H atom bound rovibrational states. The system exhibits a chemisorptive well-depth of 755 meV, which is unfavorably high for spillover; however, an unexpected coherent quantum migration mechanism is revealed, which may account for the experimentally observed reversibility of the adsorption/ desorption kinetics, and enhancement at low temperatures and pressures. A subsequent DFT and quantum dynamics study [2], performed under more realistic conditions of full H-atom coverage, was also performed; the latter is characterized by a similar quantum migration effect, but also overall energetics that are much more favorable to spillover than the single H-atom case. [1] J. L. McAfee and B. Poirier, J. Chem. Phys. 130, 064701 (2009).

[2] J. L. McAfee and B. Poirier, J. Chem. Phys. (in press, 2010)


- 36 -

A MAGNETICALLY FOCUSED MOLECULAR BEAM OF

SPIN SELECTED ORTHO-WATER

T. Kravchuk, M. Reznikov, P. Tichonov, N. Avidor, Y. Meir, A. Bekkerman and G. Alexandrowicz

Department of Chemistry, Technion, Israel

Like hydrogen molecules, water molecules also exist as two spin isomers, ortho and para- water, with the nuclear magnetic moments of the hydrogen atoms either parallel or anti-parallel. Unlike hydrogen, separation of the two isomers is not readily available, and various attempts are being made to separate the two and study their different physical properties. In 2002, successful separation was reported using the different adsorption properties of the two spin isomers [1], however this technique is still poorly reproducible, and its origin is not fully understood [2,3]. In a recent set of experiments, we have successfully formed a focused molecular beam of spin selected ortho-water using an alternative approach –magnetic focusing of a slow molecular beam. The results we obtained and some of the exciting surface science applications made possible using this spin selected beam, will be presented in the talk. [1] V. I. Tikhonov and A. A. Volkov, Science 296, 2363 (2002).

[2] P. Kapralov, V. Artemov, A. Leskin, V. I. Tikhonov and A. A. Volkov, Bull. Lebedev Phys. Inst. 35, 221 (2008).

[3] S. L. Veber. E. G. Bagryanskaya and P. L. Chapovsky, J. Exp. Theo. Phys. 102 76 (2006).


- 37 -

ADSORBATE DIFFUSION BY HOPPING BETWEEN

NON BRAVAIS LATTICE SITES: CpH/CU(111)

B. J. Hincha, F. E. Tuddenhamb, B. A. J. Lechnerb, H. Hedgelandb, A. P. Jardineb, W. Allisonb and J. Ellisb

aDepartment of Chemistry and Chemical Biology, Rutgers University, 610 Taylor Rd, Piscataway, N.J., 08854, US

bCavendish Laboratory, JJ Thomson Avenue, Cambridge, CB3 0HE, UK

Inverse ISF decay lengths, measured along the <112̄> azzimuth, for diffusing Cp/Cu(111) at room temperature.

The unsaturated hydrocarbon cyclopentadiene (C5H6, CpH) molecule readily undergoes dissociative adsorption, through proton loss, on a Cu(111) surface. Its negatively charged anion (C5H5

-, Cp-) is aromatic and stable on copper surfaces. DFT calculations of this adsorbate system support these predictions and suggest that the most stable binding on Cu(111) is at a hollow site [1]. High-resolution helium spin-echo (HeSE) measurements indicate rapid diffusion above 130K, which exhibits a jump like mechanism [1]. In certain He scattering angle ranges the intermediate structure factor (ISF) exhibits two resolvable components, with distinct decay time constants. This decay characteristic is to be associated with a jump diffusion process between non Bravais lattice sites. A short range hopping diffusion mechanism on the network of fcc and hcp hollow sites requires alternating jumps between two sublattices. We show that the observations are fully consistent with jump diffusion between these two hollow site sublattices [2]. Comparison of the experiment with derived analytical expressions for the component line widths suggests that the fcc and hcp adsorption sites are degenerate, again in complete agreement with DFT calculations [1]. Molecular dynamic simulations over a potential energy surface also display the two component ISF decays, and accurately reproduce the experimental observations. Finally, comparisons will be made of the line width characteristics expected for diffusion between other adsorption site types on an fcc(111) surface. [1] H. Hedgeland, B. A. J. Lechner, F. E. Tuddenham, A. P. Jardine, W. Allison, J. Ellis, M. Sacchi, S. J. Jenkins, B.J. Hinch, Phys. Rev. Lett. (submitted, 2010).

[2] F. E. Tuddenham, H. Hedgeland, A. P. Jardine, B. A. J. Lechner, B. J. Hinch and W. Allison, Surf. Sci. (submitted, 2010).


- 38 -

ENERGY-LOSS RAINBOWS AND DIFFRACTION

IN HEAVY ATOM SURFACE SCATTERING

J. M. Moixa, E. Pollaka and S. Miret-Artésb

aChemical Physics Department, Weizmann Institute of Science,76100 Rehovoth, Israel bInstituto de Física Fundamental, Consejo Superior de Investigaciones Científicas,

Serrano 123, 28006 Madrid, Spain

The dynamics of a heavy particle colliding with a periodic surface is typically well described by classical mechanics. In this case, the familiar rainbow features appear in the scattering distributions. Analogous to angular and rotational rainbows, here we introduce the concept of “energy-loss rainbows” which appear as multiple maxima in the final energy distribution of the scattered particle. Evidence is provided that they may have been observed in Ne scattering from self-assembled monolayers. However, in some situations the classical description is not adequate and quantum effects cannot be ignored even for the scattering of heavy particles from surfaces. For example, recent work in molecular interferometry has demonstrated that one may observe interference of very heavy species passing through a grating. It is demonstrated that surfaces may provide a natural “grating” with which to observe quantum diffraction of heavy particles. Through model calculations we show that the effect is robust with respect to the incident energy, the angle of incidence and the mass of the particle


- 39 -

DYNAMICS OF MOLECULAR AND POLYMERIC INTERFACES PROBED

WITH ATOMIC BEAM SCATTERING AND SPM IMAGING

J. Beckera, R. Browna, M. Freedmana, E. Johanssonb, N. S. Lewisb and S. J. Sibenera

aJames Franck Institute and Department of Chemistry,

The University of Chicago, 929 East 57th Street, Chicago, IL 60637 bBeckman Institute and Kavli Nanoscience Institute, Division of Chemistry and Chemical Engineering,

210 Noyes Laboratory, 127-72, California Institute of Technology, Pasadena, CA 91125

The scattering of atomic and molecular beams from well-characterized surfaces is an incisive method for studying the dynamics of gas-surface interactions, providing precise information on the energy and momentum exchange mechanisms which govern such encounters. They also serve as precision tools for examining the properties of clean, adsorbate decorated, and thin-film covered interfaces. Strategic objectives are to extend, quite significantly, the scope and precision of such scattering studies to include complex interfaces, encompassing crystalline, glassy, structurally-dynamic, and amorphous materials. We also seek to improve understanding of interfacial condensation and reactivity. Scanning probe imaging is being used to augment the scattering data, helping to visualize local events on atomic and nano length scales.

We report on several recent accomplishments: (i) building upon our initial studies of collisional energy transfer at polymeric interfaces as a function of composition (PMMA, PS, PB), molecular weight, thickness & nanoconfinement, temperature, and annealing [1-3], we are examining the surface dynamical properties of PET polymer thin films in their glassy vs. crystalline phases [4], and are elucidating for the first time clear changes in the energy accommodation characteristics due to such polymer structural changes; (ii) helium atom scattering has been used to measure the surface structure and vibrational dynamics of (1x1) CH3- and CD3-terminated Si(111) [5]. The high quality of the observed diffraction patterns indicate a high degree of long-range ordering for this novel, atmospherically stable, and technologically interesting interface, while inelastic measurements have quantified the lateral and perpendicular displacements –with energy accommodation being dominated by local Si-CH3 librations; (iii) we have used scattering measurements combined with glancing angle in situ Fourier Transform IR spectroscopy to examine the sticking and reflectivity of water interacting with ice films [6]. These studies are revealing details of condensation occurring under non-equilibrium conditions. If time permits, closing comments will also be made on very recent supersonic and hyperthermal [7] neutral atom scattering experiments in which Xe is used to gently sputter ice films in order to understand the energy transfer processes that govern such interactions.

[1] M. A. Freedman, A. W. Rosenbaum and S. J. Sibener, Phys. Rev. B 75, 113410 (2007).

[2] M. A. Freedman, J. S. Becker, A. W. Rosenbaum and S. J. Sibener, J. Chem. Phys. 129, 44906 (2008).

[3] M. A. Freedman, J. S. Becker and S. J. Sibener, J. Phys. Chem. B 112, 16090 (2008).

[4] J. S. Becker, R. D. Brown, D. R. Killelea, H. Yuan and S. J. Sibener, PNAS, DOI 1008268107.

[5] J. S. Becker, R. D. Brown, Erik Johansson, N. S. Lewis and S. J. Sibener, J. Chem. Phys. (in press, 2010).

[6] K. D. Gibson, D. R. Killelea, H. Yuan and S. J. Sibener, J. Chem. Phys. (submitted, 2010).

[7] K. D. Gibson and S. J. Sibener, J. Phys. Chem. C 113, 13325 (2009).


- 40 -


- 41 -

CONTRIBUTED TALKS

ABSTRACTS


- 42 -


- 43 -

ANGULAR INTENSITY DISTRIBUTIONS OF N2 AND CO SCATTERED

FROM GRAPHITE SURFACE

J. Oh, T. Kondo, D. Hatake, Y. Honma, K. Arakawa, T. Machida and J. Nakamura

Institute of Frontier Science, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8573, Japan

The graphite surface consists of the π conjugated system which originates from the resonance of the 2pZ electron orbital of the carbon atoms. When the π conjugated system is broken, the specific electronic states, “the non-bonding π electronic states”, are known to form on the surface. The non-bonding π electronic states at the Fermi level of the graphite-related materials are of special interest to the wide variety of fields in the science. We have reported that the modification of the local electronic structure of the graphite surface significantly affects the gas-graphite interaction based on the measurements of the angular intensity distributions of He and Ar beam scattered from the pristine and the defect induced (Ar+ ions sputtered)! graphite surfaces [1]. From the He scattering results, the cross-section for the He diffuse scattering per defect is estimated as much as 113 nm2. The origin of the extremely large cross-section is ascribed to the modulated electronic states of graphite around the defect based on the STM measurements, which is due to the local breaking of the π conjugated system of graphite. In the case of Ar scattering, the new component appears in the scattering distribution of Ar for the defect induced graphite surface. The component has a larger peak position angle than that for the pristine graphite surface, indicating that the normal component of the translational energy of Ar atom was much lost by the collision at the electronically modified area of graphite. In this work, we have measured angular intensity distributions of N2 and CO beams scattered from the pristine and defect induced graphite surfaces, in order to investigate the effects of the molecular structure on the gas-graphite interaction. Although N2 and CO molecules have the same molecular weight, it is well known that these molecules show different scattering features. The difference has been attributed to the deviation of the center-of-mass position of CO from the molecular center [2]. On the graphite surface, however, any differences in angular intensity distributions of N2 and CO are found under our wide-range experimental conditions. This counterintuitive coincidence of the distribution is ascribed to the characteristic behavior of graphite which consists of two-dimensional layers of light carbon atoms. The detail of each scattering feature and the effects of the electronic modification of graphite on the scattering event will be discussed in detail in the presentation with results of calculation. [1] J. Oh, T. Kondo, D. Hatake, Y. Honma, K. Arakawa, T. Machida and J. Nakamura, J. Phys.: Condens. Matter 22, 304008 (2010).

[2] T. Kondo, H. S. Kato, T. Yamada, S. Yamamoto and M. Kawai, Eur. Phys. J. D 38, 129 (2006).


- 44 -

MULTIFACETED DYNAMICAL APPROACH TO ADSORPTION IN SURFACES

A. S. Sanza, R. Martínez-Casadob and S. Miret-Artésa aInstituto de Física Fundamental – CSIC, Serrano 123, 28006 Madrid, Spain

aDepartment of Chemistry, Thomas Young Centre, Imperial College, London SW7 2AZ, UK

Surface adsorption processes are involved in many different well-known applications from everyday life, such as lubrication, glues, catalytic reactions (eg., in the automobile or the pharmaceutical industries), aerodynamics (eg., ceramic and anti-oxidizing covers), crystal growth (e.g., lithography), etc. Therefore, many efforts have been and are put to the study of this process, encompassing the attachment and detachment of atoms, molecules or clusters on surfaces as well as the motion of these systems through out the surface itself. From these studies one can obtain information about the surface configuration (crystal structure), the intermolecular forces mediating the interaction between the surface and the attached/detached system, or the mobility of the latter through the surface. It is therefore clear that, parallel to the development of very precise numerical techniques devoted to unravel this type information, it would be desirable to have theories and models that allow us to understand the physics involved in the corresponding processes [1,2]. The purpose of this communication is to provide an overview of different theories and models aimed at understanding the physics of adsorption processes, in particular, in two situations: (1) the temporary adsorption of probe atoms due to the presence of adsorbates on the surfaces and (2) the adsorbate motion on surface. In the first case, different models will be considered and discussed, from ray optics to Bohmian mechanics, in order to show how each one of them operates. As a working model, the dynamics of He atoms when probing a Pt(111) surface with a fixed CO adsorbate will be considered. Particular emphasis will be put on selective adsorption resonances in the spirit of the Lennar-Jones–Devonshire model, stressing the interest of the Bohmian interpretation, which provides a physical insight without abandoning the quantum framework [3,4], as happens with other classical or semiclassical models. In the second case, the diffusion of Na atoms on Cu(001) surfaces is considered, focussing on the information that can be obtained through phenomenological stochastic approaches within the context of the theory of open quantum systems [5-7]. [1] R. Guantes, A. S. Sanz, J. Margalef-Roig and S. Miret-Artés: Surf. Sci. Rep. 53, 199 (2004).

[2] A. S. Sanz and S. Miret-Artés: Phys. Rep. 451, 37 (2007).

[3] A. S. Sanz, F. Borondo and S. Miret-Artés: Phys. Rev. B 69, 115413 (2004); J. Chem. Phys. 120, 8794 (2004).

[4] A. S. Sanz and S. Miret-Artés: J. Chem. Phys. 122, 014702 (2005).

[5] R. Martínez-Casado, J. L. Vega, A. S. Sanz and S. Miret-Artés: Phys. Rev. Lett. 98, 216102 (2007); J. Phys.: Condens. Matter 19, 305002 (2007); Phys. Rev. B 77, 115414 (2008).

[6] R. Martínez-Casado, A. S. Sanz, S. Miret-Artés: J. Chem. Phys. 129, 184704 (2008).

[7] R. Martínez-Casado, A. S. Sanz, J. L. Vega, G. Rojas-Lorenzo and S. Miret-Artés, Chem. Phys. 370, 180 (2010).


- 45 -

CLASSICAL THEORY OF ROTATIONAL RAINBOW SCATTERING

FROM UNCORRUGATED SURFACES

Yu. Khodorkovsky, I. Sh. Averbukh and E. Pollak Chemical Physics Department, Weizmann Institute of Science, 76100 Rehovoth, Israel

A classical perturbation theory is developed to study rotational rainbow scattering of molecules from uncorrugated frozen surfaces [1]. Considering the interaction of the rigid rotor with the translational motion towards the surface to be weak allows for a perturbative treatment, in which the known zeroth order motion is that of a freely rotating molecule hitting a surface. Using perturbation theory leads to explicit expressions for the angular momentum deflection function with respect to the initial orientational angle of the rotor that are valid for any magnitude of the initial angular momentum. The rotational rainbows appear as peaks both in the final angular momentum and rotational energy distributions, as well as peaks in the angular distribution, although the surface is assumed to be uncorrugated. The derived analytic expressions are compared with numerical simulation data. Even when the rotational motion is significantly coupled to the translational motion, the predictions of the perturbative treatment remain qualitatively correct.

[1] Y. Khodorkovsky, I. Sh. Averbukh and E. Pollak, J. Phys.: Condens. Matter 22, 304004 (2010).


- 46 -

MULTIFACETED DYNAMICAL APPROACH TO ADSORPTION IN SURFACES

P. Kolea, H. Hedgelanda, A. P. Jardinea, W. Allisona, J. Ellisa and G. Alexandrowicza aCavendish Laboratory, University of Cambridge, Cambridge, UK

bSchulich Faculty of Chemistry, Technion – Israel Institute of Technology, Haifa, Israel

Helium Spin Echo is a powerful technique for measuring surface dynamics on atomic length-scales with high temporal resolution [1]. Besides adsorbate diffusion, the technique can also be employed for studying inelastic processes, such as surface phonons and adatom vibrational modes. A unique property of Spin Echo is its ability to measure scattered intensity as a function of both incoming and outgoing wavelengths [2], known as the two-dimensional wavelength intensity matrix, containing all information about elastic and inelastic scattering processes. The approach is independent of incident beam energy and therefore attains ultra high energy resolution. Here we present the first measurement of a two-dimensional wavelength intensity matrix, performed on the Rayleigh mode of a Cu(111) crystal of which the dispersion relation is well known [3]. The conditions were chosen such that the phonon peak and elastically scattered intensity are very narrowly spaced, making it extremely difficult for other techniques to separate and identify the two peaks. In the matrix measured with the Spin Echo technique, two separate features are clearly visible, corresponding to the Rayleigh mode and elastically scattered intensity. The main advantage of the 2D intensity matrix over traditional phonon measurements is that line shapes and peak positions can be obtained directly as a function of incident energy, without the need for deconvolving experimental influences. We discuss the benefits and difficulties of the technique and compare them with results of 1D phonon measurements. [1] A. P. Jardine, H. Hedgeland, G. Alexandrowicz, W. Allison and J. Ellis, Prog. Surf. Sci. 84, 323 (2009).

[2] G. Alexandrowicz and A. P. Jardine, J. Phys. Cond. Matt. 19, 305001 (2007).

[3] U. Harten, J. P. Toennies and Ch. Wöll, Faraday Discuss. Chem. Soc. 80, 137 (1985).


- 47 -

HIGHLY ORDERED WATER STRUCTURES ON

AN OXYGEN PRECOVERED RUTHENIUM SURFACE

N. Avidora, H. Hedgelandb, G. Heldc, A. P. Jardineb, W. Allisonb, J. Ellisb T. Kravchuka and G. Alexandrowicza

aShulich Faculty of Chemistry, Technion, Haifa 32000, Israel bCavendish Laboratory, University of Cambridge, Madingley Road, Cambridge, CB3 0HE, UK

cDepartment of Chemistry, University of Reading, Whiteknights, RG6 6AD, UK

We present helium scattering measurements of a water ad-layer grown on a O(2x1)/Ru(0001) surface. The adsorbed water layer results in a well ordered helium diffraction pattern with systematic extinctions of diffraction spots due to glide line symmetries. The data reflects a well defined surface structure which maintains proton order even at surprisingly high temperatures of 140K. The diffraction data we measure is consistent with a structure recently derived from STM measurements performed at cryogenic temperatures. Comparison with recent DFT calculation is in partial agreement, suggesting that these calculations might be underestimating the contribution of relative water molecule orientations to the binding energy.


- 48 -

BOHMIAN MECHANICS WITH COMPLEX ACTION: APPLICATION TO NONADIABATIC TRANSITIONS

N. Zamstein, Y. Kurzweil and D. J. Tannor Department of Chemical Physics, Weizmann Institute of Science, Rehoboth 76100, Israel

In the 1950’s, David Bohm, building on earlier work by de Broglie and Madelung, developed an exact formulation of quantum mechanics based on quantum trajectories. In recent years, a great deal of effort has been devoted to exploring whether Bohmian mechanics (BM) can be a useful numerical tool for calculating quantum dynamics in complex systems. The biggest numerical obstacle has been the calculation of the “quantum force”, into which all the non-locality of quantum mechanics enters. We have recently developed a new formulation of Bohmian mechanics, called Bohmian Mechanics with Complex Action (BOMCA) in which the quantum action, S, is complex. BOMCA requires the propagation of complex trajectories, but the size of the quantum force is typically much smaller than in the conventional BM. This talk will discuss the application of BOMCA to non-adiabatic transitions. When multiple potential surfaces are introduced into the BOMCA equations it emerges that trajectories evolve with different (complex) dynamics on the two potential surfaces. Recently, non-adiabatic scattering of the NO molecule from a Au(111) surface has been studied using a surface hopping technique by Tully and co-workers, and it was found that molecule-surface forces can steer the molecule into strong-coupling configurations. In our method there is no surface hopping: trajectories on different surfaces interact by influencing the phase of their counterparts on the other surface. We illustrate the approach by applying it to two benchmark systems introduced by Tully.


- 49 -

GAUSSIAN FLEXIBILITY WITH FOURIER ACCURACY:

THINKING INSIDE THE BOX

A. Shimshovitz and D. J. Tannor Department of Chemical Physics, Weizmann Institute of Science, Rehoboth 76100, Israel

We propose a new method for solving quantum mechanical problems, which combines the flexibility of Gaussian basis set methods with the numerical accuracy of the Fourier method. The method is based on the use of the von Neumann (vN) basis of phase space Gaussians. Despite the formal completeness of the vN basis, previous attempts to use this basis in quantum calculations have been plagued with numerical errors. By incorporating periodic boundary conditions into the von Neumann basis (pvN) we obtain exact equivalence with the highly stable and accurate Fourier Grid Hamiltonian (FGH) method. We focus on the time-independent Schrödinger equation and show results for the harmonic, Morse and Coulomb potentials that demonstrate that the pvN basis is significantly more accurate than the usual vN method. Furthermore, by using a basis biorthogonal to the periodic Gaussians (bvN) we are able to remove basis functions without significant loss of accuracy and obtain much higher efficiency than in the FGH. We show that in the classical limit the method has the remarkable efficiency of 1 basis function per 1 eigenstate. In the next stages we intend to test the method on helium in six dimensions and to extend the method to time-dependent quantum mechanics. Although it is still in its initial stages of development, the method could ultimately provide a route to more accurate and efficient calculations of surface electronic structure and dynamics.


- 50 -


- 51 -

LIST OF PARTICIPANTS

Gil ALEXANDROWICZ [email protected]

William ALLISON [email protected]

Micha ASSCHER [email protected]

Ilya Sh. AVERBUKH [email protected]

Navad AVIDOR [email protected]

Asaf AZURI [email protected]

Giorgio BENEDEK [email protected]

Holger CARTARIUS [email protected]

Riccardo CONTE [email protected]

Shauli DAON [email protected]

John ELLIS [email protected]

Daniel FARÍAS [email protected]

Benny GERBER [email protected]

Nicholas M. HARRISON [email protected]

Yong HE [email protected]

Jane HINCH [email protected]

Barak HIRSHBERG [email protected]

Bodil HOLST [email protected]

Reuven IANCONESCU [email protected]

Yuri KHODORKOVSKY [email protected]

Eli KOLODNEY [email protected]

Pepijn KOLE [email protected]

Takahiro KONDO [email protected]

Leeor KRONIK [email protected]

Tatyana KRAVCHUK [email protected]

Didier LEMOINE [email protected]

Richard MANSON [email protected]

mailto:[email protected]










https://webmail.csic.es/imp/compose.php?to=yuri.khodorkovsky%40weizmann.ac.il&thismailbox=INBOX&Horde=bj6dbkrqc6n3kr1210cfhpanc7







- 52 -

Ruth MARTÍNEZ-CASADO [email protected]

Timothy K. MINTON [email protected]

Salvador MIRET-ARTÉS [email protected]

Jeremy M. MOIX [email protected]

Junepyo OH [email protected]

Uri PESKIN [email protected]

Bill POIRIER [email protected]

Eli POLLAK [email protected]

Peter SAALFRANK [email protected]

Ángel S. SANZ [email protected]

Asaf SHIMSHOVITZ [email protected]

Steven J. SIBENER [email protected]

David J. TANNOR [email protected]

Peter TOENNIES [email protected]

John C. TULLY [email protected]

Christof WÖLL [email protected]

Noa ZAMSTEIN [email protected]


https://webmail.csic.es/imp/compose.php?to=s-ojpaul%40ims.tsukuba.ac.jp&thismailbox=INBOX&Horde=bj6dbkrqc6n3kr1210cfhpanc7







Documents

BOOK OF ABSTRACTSfama.iff.csic.es/con/SAMS-2010/SAMS-files/Book_of...Rather unexpected new information on the electron phonon coupling comes from Inelastic Helium Atom Scattering (IHAS)