# 5.05 – Photoelectron Spectroscopy (PES)

A specific aspect of chemistry used to provide additional evidence for quantum theory is that of photoelectron spectroscopy (PES).  Today, we will go into PES and become familiar with the information presented in PES line spectra.

Lesson Objectives

• Describe PES and how it provides better evidence than successive ionization for the existence of orbitals
• Solve problems related to PES spectra

This concept is presented in the text, but you will find a more specific breakdown of the ideas in the slide set below.  Take notes and complete the practice tasks before continuing on to the next stage of this mission.

Work out the problems below, and check your work before submitting it into OneNote.

1. Consider the simulated PES plot shown below, that is produced by the analysis of the atoms of a single element. All peaks in the PES are shown.

1. Using the plot, suggest the electron configuration of the element and identify the element.
2. Which two peaks are likely to represent electrons that are most likely to be removed when these atoms form ions?
3. Using your answer in (b), identify the most likely charge on an ion of this element.
4. Suggest a reason for the huge jump in energy between the peak at 12.1 and the peak at 150.
5. Suggest a reason for the x-axis being labeled with increasing values from right to left.

1. Consider the simulate PES plot shown below, that is produced by the analysis of the atoms of a single element. All peaks in the PES are shown.

1. Write the electron configuration and identify the element.
2. The plot is divided into three separate areas on the x-axis. Why is the axis divided in this manner?
3. What would be the charge on an ion formed from this atom? Justify your answer.
4. What is the significance of three peaks having the same height?
5. The peaks at 1.25 and 2.44, as well as the peaks at 20.2 and 26.8, are relatively close to one another but have different energies. Explain why they are of the same magnitude but are slightly different.

1. Consider a PES plot for carbon atoms.
1. How many peaks would you expect in the PES for carbon?
2. What would be the relative heights of the peaks you have identified in (a)? Explain your answer carefully.
3. How would you expect the height of the 2p peak in carbon’s PES to compare to the height of the 2p peak in nitrogen’s PES?

All done with spectoscopy for now.  Time to resume our look at energy in the next mission!