Ok Photons have Spin 1... therefore they have j=1
but i guess you can also explain it through expanding the dipole radiation into sperical harmonics and that only those with l=1 can express a dipole or something... could that be it?
hey,
I was asking myself a few questions about the selection rules for EM dipole radiation which occurs if electrons "jump" into lower bound states according to the selection rules.
now I know that the full explanation about matrix elements of the dipole operator comes from fermi's golden...