[chilli]

Hello all!
I was asked to draw an MO diagram of O₂ in its excited state and I'm stuck, i have no idea how it should look like
I know its configuration is suppose to be 2s²sp³3s¹ but I cant seem to understand how this works, I made a regular O₂ MO diagram that looks something like this:



How do I represent it in its excited state tho?
Thx in advance for any suggestions!

[chilli]

oh, why was my link deleted?
I would have uploaded my diagram but couldn't find an "upload from computer" button

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[chilli]

ah! cool ty!
there's my modest one 
anyone has some kind of lead? hint?
would appreciate any kind of direction

[Corribus]

There is some ambiguity in defining the first excited state of oxygen just from the MO diagram. Hund's rules can provide a guide, but it's not readily apparent to most people.

This Wikipedia article provides you with more information:

https://en.wikipedia.org/wiki/Singlet_oxygen

[chilli]

well that's tricky...
so the fact that O₂ is para magnetic is hinting to this situation?
ty very much for the link!

[Corribus]

The fact that oxygen is a g.s. triplet means that there are multiple excited states having nominally the same orbital configuration but different energies by virtue of possible spin states. E.g. the ¹Σ_g⁺ (ground) and ³Σ_g^- (excited) states have the same electron orbital configurations but are separated by about ~160 kJ/mol in energy. The ¹Δ_g state - the lowest excited state, 95 kJ/mol above the ground state - has a slightly different orbital configuration (which is why the term symbol looks different).

If the question only asked you to draw any excited state, then this is fairly simple and there are lots of possible answers. However if you need to draw the lowest excited state, this is more challenging. I don't think it is necessarily readily apparent which of the excited states is lower in energy by simple inspection of an MO diagram. A nuanced reading of Hund's rules is required.

[chilli]

It wasn't specified and I'm very early in my studies so maybe it did mean any excited state, I got even more confused now, would a case with both electrons in σ2p* would be acceptable?

[Corribus]

Yes, that would qualify as an excited state.
In most cases, however, you would answer this question by simply promoting just one of the (ground state) electrons into a higher energy orbital.

[Enthalpy]

If you're early in your studies, the expected answer could well be that both electrons paired on the same 2p_x mean a higher energy than one on 2p_x an the other on 2p_y.

[chilli]

ok, I chose this one, seemed simpler, found it hard trying to explain why electron py would jump into px orbital  (why would it?)
what will determine where it will jump? would a certain amount of energy yield different arrangements?
and ty all for the answers! u are a great *delete me* and sorry for all the questions that every answer seems to create...

[Corribus]

ok, I chose this one, seemed simpler, found it hard trying to explain why electron py would jump into px orbital  (why would it?)
what will determine where it will jump?

That would require a long explanation that is definitely far above the high school level. The most obvious and basic thing that determines what orbital (state) an electron will transition to is energy, which must (closely) match the difference in energy between the ground state and excited state. This is called the Bohr condition, and is one (but not the only) condition that determines the probability that a transition will happen.

[Enthalpy]

found it hard trying to explain why electron py would jump into px orbital  (why would it?)

Paths for the production of this "singlet oxygen" are given there
https://en.wikipedia.org/wiki/Singlet_oxygen#Production
it involves further molecules. Light for instance won't let an electron change from p_y to p_x.

[chilli]

ty both so much!
looked it up and found this https://www.youtube.com/watch?v=1vJYJgQN9Ls, so cool, really looking forward to get to lab lessons.