PES Lecture1 History

8/8/2019 PES Lecture1 History

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Photoelectron Spectroscopy

Lecture 1: Development of PhotoelectronSpectroscopy

Photoionization Koopmans Theorem

Brief Historical Overview

Current Topics


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Ionization occurs when matter interacts with light ofsufficient energy (Heinrich Hertz, 1886)(Einstein, A. Ann. Phys. Leipzig 1905, 17, 132-148.)

Ehn = electron kinetic energy + electron binding energy

hn

e- e-e-

Photoelectric Effect

Photoelectron spectroscopy uses this phenomenon

to learn about the electronic structure of matter


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General Overview of Spectroscopy

Spectroscopy uses interaction of electromagneticradiation with matter to learn something about thematter.

If electromagnetic radiation present is in resonance withthe energy spacing between different states (electronic,vibrational, rotational, etc) of matter, radiation will beabsorbed and transitions will occur.

The radiation that is transmitted through the sample ismeasured, and spectrum can be reported as eithertransmittance or absorbance of radiation.

Photoelectron spectroscopy is entirely different!


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Photoelectron vs Other

SpectroscopiesOthers Photon must be in

resonance with transition

energy Measure absorbance or

transmittance of photons

Scan photon energies

Photoelectron Photon just needs enough

energy to eject electron

Measure kinetic energy ofejected electrons

Monochromatic photonsource


5/17

Why would a chemist care about

ionizations anyway? Models for description of electronic structure are

typically based on an orbital approximation. Tjalling C. Koopmans, "Ordering ofWave Functions and

Eigenvalues to theI

ndividual Electrons of an Atom."Physica 1933, 1, 104 Koopmans Theorem: The negative of the energy of an

occupied orbital from a theoretical calculation is equal tothe vertical ionization energy due to the removal of anelectron from that orbital.

!=N

i

iJ )(.).(

iiEI JI!


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Ionization is still a transition

between states Initial State: Neutral (or anion)

Final State: Atom/Molecule/Anion after anelectron is removed, plus the ejected electron

M M+ + e-

More on this next time


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Historical Timeline

First spectrophotometer: 1850s

First IR:1880s

First crystallography: 1912 First NMR: 1938

First EPR: 1944

First PES: 1957


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What took so long?

Development of electron kinetic energyanalyzers with sufficient resolution to be useful.

Development of suitable sources of ionizingradiation vacuum UV, soft X-ray

Development of electron detectors

Development of UHV technology


9/17

First Ionization Energies: cesium 3.89 eV (319 nm)ferrocene 7.90 eV (157 nm)

water 12.61 eV (98 nm)


10/17

Kai Seigbahn: Development of

X-ray Photoelectron Spectroscopy

Nobel Prize in Physics 1981(His father, Manne Siegbahn, won the Nobel Prize in Physics in 1924for the development of X-ray spectroscopy)

C. Nordling E. Sokolowski and K. Siegbahn, Phys. Rev. 1957, 105, 1676.


11/17

Electron Spectroscopy for

Chemical Analysis (ESCA)S. Hagstrm, C. Nordling and K. Siegbahn, Phys. Lett. 1964, 9, 235.


12/17

David Turner: Development ofUltraviolet Photoelectron Spectroscopy

D.W. Turner and M.I. Al Jobory, J. Chem. Phys. 1962, 37, 3007


13/17

Current Topics ofInterest:

high resolution


14/17


angular dependence

800 nm

400 nm

CS2 photoelectron images(Abel inverted)


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variable photon studies


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applications to chemical problems

NN

9 8 7 6 5Ionization Energy (eV)

NNMabrMb

Q-

Adiabatic States

=- = (1/2)(=a - =b)

=+ = (1/2)(=a + =b)

Hab =

IE1

IE2

2Hab

IE2

IE2IE1

IE1


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Summary

PES is a fairly new technique, continuingto develop

PES has unique features compared toother spectroscopies

Valence spectroscopy: information onbonding

Core spectroscopy: qualitative andquantitative analysis, chemical shift

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PES Lecture1 History