Photoelectron Spectroscopy

(PES)

Spectroscopy

• Method of analyzing matter using electromagnetic radiation.

Photoelectron Spectroscopy

• PES apparatus:

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iramis.cea.fr

Photoelectron Spectroscopy

How it works:

1. Sample is exposed to EM radiation
2. Electrons jump out of sample and go through analyzer

http://chemwiki.ucdavis.edu

PES Data

Energy to remove an electron

(binding energy)

(increases to the left!)

🡨

Number of electrons

Electrons generally farther from the nucleus

Electrons

generally closer to the nucleus

The bigger the peak – the more electrons

Each peak represents the electrons in a single sublevel in the atom

Hydrogen vs. Helium

Hydrogen

Helium

The helium peak is twice as tall because there are twice as many electrons in the 1s sublevel

1 electron in 1s

2 electrons in 1s

#e^-

🡨 energy

#e^-

🡨 energy

Hydrogen vs. Helium

Hydrogen

Helium

The helium peak is farther to the left (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)

1 electron in 1s

2 electrons in 1s

#e^-

🡨 energy

#e^-

🡨 energy

Oxygen (1s²2s²2p⁴)

Energy to remove an electron

(binding energy)

(increases to the left!)

🡨

Number of electrons

2 electrons in 1s

2 electrons in 2s

4 electrons in 2p

Scandium (1s²2s²2p⁶3s²3p⁶4s²3d¹)

Energy to remove an electron

(binding energy)

(increases to the left!)

🡨

Number of electrons

2 in1s

2 in 2s

2 in 4s

6 in 2p

2 in 3s

6 in 3p

1 in 3d

*Notice that it takes more

energy to remove an electron from

3d than from 4s.

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This is because as electrons are

added to 3d they shield 4s thus it’s

easier (takes less energy) to remove

4s electrons compared to 3d

electrons.

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Remember when transition metals make

positive ions - it’s the s electrons that are

lost first!

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Example 1:

Energy

🡨

Number of electrons

Identify the element whose

PES data is shown to the right.

Sodium

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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

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In which sublevel are the electrons

Represented by peak A

3s

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A

Example 2:

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 right?

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It takes less energy to remove a 1s electron from nitrogen because it has a lower

Effective nuclear charge (less protons) than oxygen

Example 3:

Energy

🡨

Number of electrons

Draw the expected PES

Spectrum for the element boron

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