There are spectroscopy selection rules marking some radiative electronic transitions as forbidden. For example, it is stated that single electron of H atom can not move from S2 to S1, or from P2 to S2 (and vice versa) with photon emission/absorption.
But is this true in the case of collisional (or, more generally, radiationless) transitions? Are there any selection rules and what they are if any?
I found the Wigner spin conservation rule. Are there any more rules?