Re: paired or unpaired when electron jumps to higher orbital?

"George J Bugh" <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>...
> If a paired electron is excited to jump to an orbital that is a higher
> energy state and then fails down to a metastable state, then during either
> of these states that are different from its original ground state, will its
> spin still be completely compensated or will it be at least partially
> susceptible to an external stimulus to allow electron spin resonance related
> absorption and radiation? If it becomes partially uncompensated so as to be
> susceptible to EPR techniques then how uncompensated does it become?
> 
> Thanks, George J Bugh

This process is called intersystem crossing. It forms the basis of
phosphorescence as contrasted to fluorescence. In fluorescence, the
excited state has the same spin multiplicity as the ground state, so
that the excited state decays into the ground state within less than a
ps. In phosphorescence, the excited singlett state decays into an
excited triplett state first. This can decay only very slowly to the
ground state as the transition is forbidden.

Another class of experiments is called CIDNP or CIDEP. There, you
break a molecule  in a magnetic field into two parts by radiating
it.The magnetic field will eventually change the spin of the system
from singlett to triplett, so that recombination becomes forbidden.
Can be followed in an NMR or EPR spectrometer.