Microsolvation of -propiolactone as revealed byChirped-Pulse Fourier Transform Microwave Spectroscopy

Justin L. Neill, Matt T. Muckle, Daniel P. Zaleski, Brooks H. Pate Department of Chemistry, University of Virginia, McCormick Rd, P.O. Box 400319, Charlottesville, VA 22904

I. Peña, C. Perez, J.L. Alonso Grupo de Espectroscopía Molecular (GEM), Departamento de Química Física y Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, E-47005 Valladolid, Spain

High-Resolution Spectroscopy of Solvated Organic Molecules

(H2O)3-6: Saykally group (THz tunneling)

C.J. Gruenloeh et al., Science 276, 1678 (1997).Ch. Janzen et al., J. Chem. Phys. 110, 9898 (1999).B. Ouyang, T.G. Starkley, B.J. Howard, J. Phys. Chem. A 111, 6165 (2007).D. Priem, T.-K. Ha, A. Bauder, J. Chem. Phys. 113, 169 (2000).S. E. Novick, Bibliography of Rotational Spectra of Weakly Bound Complexes, (2010). Electronic updates are available on the web at http://www.wesleyan.edu/chem/faculty/novick/vdw.html.

Water cubes: -benzene-(H2O)8: Gruenloeh et al. -phenol-(H2O)7,8: Janzen et al. (UV/IR)

Microwave studies: -trifluoroacetic acid-(H2O)3: Ouyang et al. -formic acid-(H2O)2

: Priem et al.

Experimental Methods:Chirped-Pulse FTMW Spectrometer

1.23 million averages (59 h), 300 W TWTA2 nozzles, 10 FIDs per valve injection

He or Ne backing gas (4 atm)

G.G. Brown, B.C. Dian, K.O. Douglass, S.M. Geyer, S.T. Shipman, and B.H. Pate, Rev. Sci. Instrum. 79 (2008) 053103L. Alvarez-Valtierra, S.T. Shipman, J.L. Neill, B.H. Pate, A. Lesarri, ISMS 2008, WF12.T. Emilsson, H.S. Gutowsky, G. de Oliveira, C.E. Dykstra, J. Chem. Phys. 112, 1287 (2000).

Tools for structural analysis:-10% H2

18O sample to observe isotopically substituted species-CP-FTMW Stark effect measurement (60 V/cm) calibrated with trifluoropropyne 1st-order shifts

x50

x500 x5000

CP-FTMW Spectrum

Dense spectrum—microwave-microwave double resonance spectroscopy used extensively

1966 lines detected with signal to noise > 3:1

1197 lines (61%) still unassigned

x230

CP-FTMW Spectrum

-propiolactone

Experimental Ab Initio Pct. Error

A (MHz) 12405.9884(13) 12372.59 -0.27%

B (MHz) 5244.4548(5) 5240.17 -0.08%

C (MHz) 3869.1913(4) 3864.47 -0.12%

A (D) 3.675(10) 3.74 1.8%

B (D) 2.01(5) 2.07 2.9%

C (D) --- 0.00 ---

total (D) 4.19 4.28 2.1%

Ab Initio calculations: Gaussian 03W, mp2/6-311++g(d,p) (all structures)Spectral fits: SPFIT/SPCAT, PIFORM (PROSPE, Z. Kisiel, http://www.ifpan.edu.pl/~kisiel/prospe.htm), QSTARK (PROSPE)Figures: PMIFST (PROSPE)N. Kwak, J.H. Goldstein, J.W. Simmons, J. Chem. Phys. 25, 1203 (1956).Z. Chen and J. van Wijngaarden, J. Mol. Spectrosc. 257, 164 (2009).

Large circles: ab initio structuresSmall circles: substitution coordinatesAvg. deviation: 0.011 Å

CP-FTMW Kwak et al.

A (D) 3.675(10) 3.67(4)

B (D) 2.01(5) 2.00(2)

-propiolactone-H2O

Experimental Ab Initio Pct. Error

A (MHz) 6792.8734(20) 6721.55 -1.05%

B (MHz) 2056.4976(5) 2091.08 1.68%

C (MHz) 1613.5724(5) 1631.76 1.13%

A (D) 0.9964(11) 0.74 -25.7%

B (D) 2.543(23) 2.45 -3.47%

C (D) [0] (fixed) 0.63 ---

total (D) 2.73 2.64 -3.30%

O deviation: 0.071 Å

No c-type transitions observed; searched for tunneling gap<500 MHz

-propiolactone-(H2O)2

Experimental Ab Initio Pct. Error

A (MHz) 2856.852(3) 2938.33 2.85%

B (MHz) 1730.192(4) 1763.43 1.92%

C (MHz) 1377.649(3) 1417.81 2.92%

A (D) 2.160(10) 2.03 -6.02%

B (D) 1.544(23) 1.36 -11.9%

C (D) 0.330(3) 0.32 -3.03%

total (D) 2.676(25) 2.46 -8.07%

average O deviation: 0.106 Å

-propiolactone-(H2O)3Experimental Ab Initio Pct. Error

A (MHz) 1861.023(6) 1915.73 2.94%

B (MHz) 1165.9916(6) 1157.19 -0.76%

C (MHz) 883.9891(5) 873.67 -1.17%

A (D) 2.357(5) 1.98 -16.0%

B (D) 0.60(13) 0.36 -40%

C (D) 0.12(8) 0.31 158%

total (D) 2.44(15) 2.03 -16.8%

14.28° 10.3° -4.0°

87.18° 81.2° -5.9°

Experimental

A (MHz) 1887.1478(18)

B (MHz) 1110.5723(12)

C (MHz) 838.6250(12)

A (D) 0.8690(24)

B (D) ---

C (D) 1.773(8)

total (D) 1.975(8)

~5x weaker than above spectrumNo structural assignment

average O deviation: 0.197 Å

-propiolactone-(H2O)4

Experimental Ab Initio Pct. Error

A (MHz) 1234.1037(7) 1253.26 1.55%

B (MHz) 931.7212(4) 951.05 2.08%

C (MHz) 830.9703(5) 846.04 1.81%

A (D) 0.5026(9) 0.54 7.44%

B (D) 3.785(11) 3.90 3.04%

C (D) 2.667(7) 2.94 10.24%

total (D) 4.657(13) 4.91 5.43%

Experimental Ab Initio Pct. Error

A (MHz) 1263.5285(10) 1313.81 3.98%

B (MHz) 933.8867(9) 964.39 3.27%

C (MHz) 828.4353(8) 828.80 0.04%

A (D) 0.9848(15) 1.32 34.0%

B (D) 4.215(19) 4.46 4.77%

C (D) 2.009(7) 2.17 8.01%

total (D) 4.772(20) 5.14 7.71%

average O deviation: 0.105 Å

2:1 intensity ratioE rel= 70.4 cm-1

-propiolactone-(H2O)4

-(H2O)4 mininum: free protons are “udud” around the ring

-BPL-(H2O)4: free protons are “uudd” around the ring--less stable by 325 cm-1

tunneling quenched by complexation

-two structures differ only by the direction of H-bonding around the ring

J.D. Cruzan, M.R. Viant, M.G. Brown, R.J. Saykally, J. Phys. Chem. A 101, 9022 (1997).M. Schütz, W. Klopper, H.-P. Lüthi, J. Chem. Phys. 103, 6114 (1995).

-propiolactone-(H2O)5

Experimental Ab Initio Pct. Error

A (MHz) 945.8879(8) 936.88 -0.95%

B (MHz) 654.1482(5) 679.85 3.93%

C (MHz) 642.1021(5) 661.64 2.95%

(B/A)2 0.27 0.77

(C/A)2 0.60 0.52

Discrepancy in relative b/c dipoles

Conclusions

All observed structures cool to minimum-energy configurations (rather than sequential addition)

Competition/compromise between water-molecule and water-water interactions

Importance of isotopic substitution, Stark effect measurements in structure determination of large water clusters -substitution structures and dipole moments agree very well with ab initio values -Use of isotopic assignments to drive ab initio (rather than the reverse)

Acknowledgements

FundingNational Science Foundation Chemistry CHE-0616660 CRIF:ID CHE-0618755

Miniesterio de Ciencia y Tecnología (Grant CTQ2006-05367)Junta de Castilla y León, Fondo Social Europeo (Grant VA012C05)

Experimental Ab Initio Error

(D) 4.189 4.28 2.05%

28.7° 29.0° 0.3°

90° 90° 0°

PL

Dipole Moment Errors

Experimental Ab Initio Error

(D) 2.727 2.64 -3.33%

68.57° 73.2° 4.6°

90° 76.2° -13.8°

PL-H2O

Experimental Ab Initio Error

(D) 2.676 2.46 -7.9%

35.56° 33.8° -1.7°

82.92° 82.5° -0.4°

PL-(H2O)2

Experimental Ab Initio Error

(D) 2.435 2.04 -16.4%

14.28° 10.3° -4.0°

87.18° 81.2° -5.9°

PL-(H2O)3

Experimental Ab Initio Error

(D) 4.657 4.914 5.5%

82.44° 82.1° -0.3°

55.07° 53.3° -1.8°

PL-(H2O)4 (stronger)

Experimental Ab Initio Error

(D) 4.772 5.133 7.6%

76.85° 73.5° -3.3°

65.10° 65.0° -0.1°

PL-(H2O)4 (weaker)

Experimental Methods:MW-MW Double Resonance Spectroscopy

CP-FTMW-MW Double Resonance Cavity FTMW-MW Double Resonance

-propiolactone-(H2O)5

(H2O)5: slightly puckered, has an “uudud” orientation of the water pentamer

BPL-(H2O)5: similar structure; internal tunneling/pseudorotation quenched by complexation

K. Liu, M.G. Brown, J.D. Cruzan, R.J. Saykally, J. Phys. Chem. A 101, 9011 (1997).