[dipesh747]

I am currently studying photo and radiation chemistry. Obviously this is all about excited state chemistry. I just read that molecular oxygens ground state exists as a triplet state, I can see with MO theory that there will be 2 lone electrons in anti bonding orbitals each with the same Ms. So am I right in thinking that if the molecule absorbs hv that it will go into an excited singlet state? (so the Ms flips) or does it go into an excited triplet state (so the electron goes into the sigma* orbital?).

[Jorriss]

I don't know much about these processes but the one thing I can add is that a photon can not change the spin of an electron. So the electron would raise from a pi* to a sigma* orbital.