Formation of Excimer Structures: Explained for Engineers

[MartinMan]

Reposting from another section...

Can anyone explain to me how an excimer is formed? Like structure wise?

Considering Xenon.
I've gathered that an excited state Xe*, ground state Xe, and a 3rd body M react resulting in an Xe* excimer + M(carrying away excess energy).

I'm struggling to find how the ground state Xe can have any reaction at all with its full valence band. Any pointers?

Thanks in advance!
PS My physics/chemistry isn't particularly advanced, I'm studying elec. engineering.

 

[Quantum Defect]

Reposting from another section...

Can anyone explain to me how an excimer is formed? Like structure wise?

Considering Xenon.
I've gathered that an excited state Xe*, ground state Xe, and a 3rd body M react resulting in an Xe* excimer + M(carrying away excess energy).

I'm struggling to find how the ground state Xe can have any reaction at all with its full valence band. Any pointers?

Thanks in advance!
PS My physics/chemistry isn't particularly advanced, I'm studying elec. engineering.

Excimers are excited state molecules where the excited state is bound, and the ground state is not bound (or weakly bound). They can be formed in electric discharges, typically under reasonably high pressures (several bar). The high pressures are needed to increase the rate of three-body "reactions" -- e.g. Xe* + Xe + M -> Xe_2* + M.

You are correct that the noble gases are closed-shell, unreactive. This is why the ground electronic state of Xe_2 is not bound. The excited states can have significant binding energies, though. You can think of the reason why, if you think about what Xe* looks like: you have a Xe+ ion core with a weakly bound (Rydberg) electron. The Xe+ has a hole in a p-orbital that can accept an electron from the other Xe (assuming that the Rydberg electron is far away). If you draw the molecular orbital picture for the Xe2* and the Xe2, you can see that the Xe2 has a bond order of zero, while the Xe2* has a bond order of 1/2 (assume that the Rydberg electron is non-bonding).

Excimer lasers are useful because they are a rather clever three-level laser, where the intermediate level (Xe2) automatically disappears when it falls apart to form isolated atoms.