Photoelectron Spectroscopy (PES)

Photoelectron Spectroscopy Slide 1 Photoelectron Spectroscopy What is PES? Photoelectron spectroscopy analyzes the kinetic energy distribution of the emitted photoelectrons to study the composition and electronic state of a sample. PES apparatus iramis.cea.fr

Photoelectron Spectroscopy Slide 2 How it works: 1. The sample is exposed to electromagnetic radiation (typically x-ray or UV photons) 2. Electrons jump off of the surface of a sample and go through an analyzer http://chemwiki.ucdavis.edu

Slide 3 Image source: Inna M Vishik http://www.stanford.edu/~ivishik/inna_vishik_files/Page452.htm

Kinetic Energy Analyzer X-ray or UV Source Kinetic Energy Analyzer 6.26 0.52 Binding Energy (MJ/mol) Slide 4 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+

Energy to remove an electron PES Data for Neon SLIDE 5 Each peak represents the electrons in a single sublevel in the atom The bigger the peak , the more electrons Electrons generally farther from the nucleus Energy to remove an electron “binding energy” often measured in eV (electron volts) 1 eV = 1.60217657 × 10-19 J Electrons generally closer to the nucleus

Oxygen (1s22s22p4) SLIDE 6 4 electrons in 2p 2 electrons in 2s

Identify the element whose PES data is shown SLIDE 7 Identify the element whose PES data is shown Sodium Why is one peak much larger than the others? This peak represents 6 electrons in the 2p sublevel The other peaks represent only 1 or 2 electrons In which orbitals are the electrons Represented by peak A? 3s A

Sketch the expected PES spectrum for Aluminum SLIDE 8

Hydrogen vs. Helium SLIDE 9 The helium peak is farther to the right (higher energy) thus more energy is needed to remove the 1s electrons in helium. They must be held more tightly because there is a higher effective nuclear charge. (Helium has 2 protons pulling on 1s but hydrogen only has 1) The helium peak is twice as tall because there are twice as many electrons in the 1s sublevel

Example: SLIDE 10 oxygen nitrogen #e- #e- energy energy The PES data above shows only the peak for the 1s electrons. Why is the peak for Nitrogen farther to the left? It takes less energy to remove a 1s electron from nitrogen because it has a lower effective nuclear charge (fewer protons) than oxygen

Portions adapted from http://teaching.shu.ac.uk/hwb/chemistry/tutorials/molspec/beers1.htm AP 2003 FRQ #5 Chemistry, Chang, 10th edition APSI 2013 OU presentation; J. Beninga Wikipedia: IR spectroscopy gifs http://wwwchem.csustan.edu/Tutorials/images/cychexol.gif http://orgchem.colorado.edu/Spectroscopy/irtutor/images/etbenzat.gif