光電子能譜的歷史—xps

1、Photoelectron Spectroscopy,Lecture 1: Development of Photoelectron SpectroscopyPhotoionization“Koopmans’ Theorem”Brief Historical OverviewCurrent Topics,Ionization occurs when matter interacts with light of sufficien

2、t energy (Heinrich Hertz, 1886)(Einstein, A. Ann. Phys. Leipzig 1905, 17, 132-148.),Ehn = electron kinetic energy + electron binding energy,hn,,Photoelectric Effect,Photoelectron spectroscopy uses this phenomenon to le

3、arn about the electronic structure of matter,General Overview of Spectroscopy,Spectroscopy uses interaction of electromagnetic radiation with matter to learn something about the matter.If electromagnetic radiation prese

4、nt is in resonance with the energy spacing between different states (electronic, vibrational, rotational, etc) of matter, radiation will be absorbed and transitions will occur.The radiation that is transmitted through t

5、he sample is measured, and spectrum can be reported as either transmittance or absorbance of radiation.Photoelectron spectroscopy is entirely different!,Photoelectron vs Other Spectroscopies,OthersPhoton must be in res

6、onance with transition energyMeasure absorbance or transmittance of photonsScan photon energies,PhotoelectronPhoton just needs enough energy to eject electronMeasure kinetic energy of ejected electronsMonochromatic

7、photon source,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 of Wave Functions and

8、Eigenvalues to the Individual Electrons of an Atom." Physica 1933, 1, 104Koopmans’ Theorem: “The negative of the energy of an occupied orbital from a theoretical calculation is equal to the vertical ionization ener

9、gy due to the removal of an electron from that orbital.”,Ionization is still a transition between states,Initial State: Neutral (or anion)Final State: Atom/Molecule/Anion after an electron is removed, plus the ejected e

10、lectronM → M+ + e-More on this next time,Historical Timeline,First spectrophotometer: 1850sFirst IR:1880sFirst crystallography: 1912First NMR: 1938First EPR: 1944First PES: 1957,What took so long?,Development of e

11、lectron kinetic energy analyzers with sufficient resolution to be useful.Development of suitable sources of ionizing radiation – vacuum UV, soft X-rayDevelopment of electron detectorsDevelopment of UHV technology,Firs

12、t Ionization Energies:cesium3.89 eV (319 nm)ferrocene7.90 eV (157 nm)water12.61 eV (98 nm),Kai Seigbahn: Development of X-ray Photoelectron Spectroscopy,Nobel Prize in Physics 1981 (His father, Manne Sieg

13、bahn, won the Nobel Prize in Physics in 1924 for the development of X-ray spectroscopy),C. Nordling E. Sokolowski and K. Siegbahn, Phys. Rev. 1957, 105, 1676.,Electron Spectroscopy for Chemical Analysis (ESCA),S. Hagstr

14、öm, C. Nordling and K. Siegbahn, Phys. Lett. 1964, 9, 235.,David Turner: Development of Ultraviolet Photoelectron Spectroscopy,D.W. Turner and M.I. Al Jobory, J. Chem. Phys. 1962, 37, 3007,Current Topics of Interest

15、: high resolution,Current Topics of Interest: angular dependence,Current Topics of Interest: variable photon studies,,,Current Topics of Interest: applications to chemical problems,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

16、,,,,,,,,,,N,,N,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,9,8,7,6,5,Ionization Energy (eV),,,,,,,,,,,,N,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,N,,,,,,Ma—br—Mb,,Q-,Adiabatic States,?- = (1/√2)(?a - ?b),?+ = (1/√2)(?a + ?b),Hab =

17、 ,,IE2,2Hab,IE2,IE2,IE1,IE1,Summary,PES is a fairly new technique, continuing to developPES has unique features compared to other spectroscopiesValence spectroscopy: information on bondingCore spectroscopy: qualitativ