15 Jul 2014

Application of MO Diagrams (and sp mixing) with Photoelectron Spectroscopy

In-Class Activity

Submitted by Abigail Hobbs Shelton, University of TN at Martin

This in-class activity is to introduce the pairing of diatomic MO diagrams and photoelectron spectroscopy (PES).  I will be testing this out in the fall, and will post how it goes.  

I introduce the photoelectron spectrometer instrumentation immediately after completing molecular orbital diagrams of homonuclear and heteronuclear diatomic molecules.  I talk through the photoelectron spectra of a hydrogen atom, a hydrogen molecule, and a helium atom, and how bands with little evidence of fine structure indicate little bonding contribution of that orbital, and that evidence of fine structure indicates more contribution to bonding.  Then the students receive the handout where they practice drawing MO diagrams of N2 and CO.  The PES is used as a tool to show that sp mixing occurs in N2 and CO as well as to evaluate whether orbitals are involved in bonding. 

I obtained copyright permissions for both of the spectra (through June 2015 for the Miessler, Fischer, Tarr figure) on the worksheet, so no need to go find those!

Learning Goals: 

Using this worksheet, a student should be able to:

construct diatomic MO diagrams

analyze photoelectron spectra and corresponding MO diagrams to determine if sp mixing occurs


Equipment needs: 


Implementation Notes: 

Students will complete this worksheet as an in-class activity.  They will have approximately 10 minutes to complete the first problem, then will pair with another student to discuss for up to two minutes before sharing/discussing their answers with the class.  They will then complete the second question in the same fashion.  This worksheet could also easily be used for a homework assignment.   

The students should be able to draw the MO diagrams of diatomic species with and without sp mixing, then evaluate the provided photoelectron spectrum to see which MO diagram agrees with the experimental data.

Time Required: 
About 20 minutes, depending on discussion and amount of help needed.
Evaluation Methods: 

This will be ungraded in-class practice to prepare them for a MO homework assignment.  I anticipate some discussion of troubles in generating the MO diagrams or interrupting the PES.

Evaluation Results: 

I will be using this during my Fall 2014 inorganic course, stay tuned. 

*Update:  My Fall 2014 Physical Inorganic course tried it out.  Some modifications have come out of their feedback, mainly the need to draw the MO diagrams with and without sp mixing so that the students can compare both to the PES.  Their main impression was that they liked learning to evaluate the PES to determine if mixing occured, rather than just memorizing where sp mixing happens.  I couldn't be happier with that outcome!

Creative Commons License: 
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