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 http://chemwiki.ucdavis.edu

Slide 2

Image source: Inna M Vishikhttp://www.stanford.edu/~ivishik/inna_vishik_files/Page452.htm

Slide 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+3+

X-ray or UV

Source

Kinetic Energy Analyzer

Kinetic Energy Analyzer

Binding Energy (MJ/mol)

6.26

0.52

Slide 4

PES Data for Neon

Energy to remove an electron “binding energy”

often measured in eV (electron volts)

1 eV = 1.60217657 × 10-19 J

0.1 1 10 100

Photo Electron Spectra

Energy

Re

lati

ve

Nu

mb

er

of

Ele

ctr

on

s

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 (1s22s22p4)

0.1 1 10 100

Photo Electron Spectra

Energy

Re

lati

ve

Nu

mb

er

of

Ele

c-tr

on

s

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 2electrons

In which orbitals are the electrons Represented by peak A?3s

0.1 1 10 100 1000

Photo Electron Spectra

Energy

Re

lati

ve

Nu

mb

er

of

Ele

ctr

on

s

A

SLIDE 7

Sketch the expected PES spectrum for

Aluminum

0.1 1

Photo Electron Spectra

Energy

Re

lati

ve

Nu

mb

er

of

Ele

ctr

on

s

0.1 1 10 100 1000

Photo Electron Spectra

Energy

Re

lati

ve

Nu

mb

er

of

Ele

ctr

on

sSLIDE 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)

0.1 1 10

Photo Electron Spectra

Energy

Re

lati

ve

Nu

mb

er

of

Ele

c-tr

on

s

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• http://teaching.shu.ac.uk/hwb/chemistry/tutorials/molspec/b

eers1.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/et

benzat.gif