Photoelectron Spectroscopy (PES)

Photoelectron Spectroscopy What is PES? o 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 Slide 1

Photoelectron Spectroscopy 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 Slide 2

Image source: Inna M Vishik Slide 3

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

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

Oxygen (1s 2 2s 2 2p 4 ) 2 electrons in 1s2 electrons in 2s4 electrons in 2p SLIDE 6

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 SLIDE 7

Sketch the expected PES spectrum for Aluminum SLIDE 8

Hydrogen vs. Helium 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 SLIDE 9

Example: nitrogen oxygen #e - energy #e - 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 SLIDE 10

Portions adapted from eers1.htm eers1.htm AP 2003 FRQ #5 Chemistry, Chang, 10 th edition APSI 2013 OU presentation; J. Beninga Wikipedia: IR spectroscopy gifs benzat.gif benzat.gif