Photoelectron+Spectroscopy

Photoelectron Spectroscopy (PES)
When an atom is struck by a photon of sufficient energy (usually UV or X-rays), the photon can 'bump' off an electron from the atom.



This is called the "photoelectric effect", and is used to study the electronic structure of the atom (or molecules).

This process will ionize the atom, and the ionization energy can be measured.



See this website for a simulation of PES.

The results of PES are usually shown in a graph of signal intensity or strength (y-axis) versus binding energy (think ionization energy; x-axis).



Some interesting points about a PES spectrum:
 * the x-axis, depicting energy, is usually backwards (goes from high to low energy).
 * the y-axis can be used to determine the number of electrons in each peak.

The example above is a PES spectrum for nitrogen. Nitrogen as an electron configuration of 1s 2 2s 2 2p 3.

The electrons closest to the nucleus, those in the 1s, will be hardest to remove (require more ionization energy). So, as you read the graph from left to right, you are getting further from the nucleus.



The peak heights therefore are representative of the number of electrons in each sublevel.

Realize that these two graphs are simulated; a real PES spectrum can be quite complex, and takes a bit of experience to analyze.



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