Recall the selection rules for purely rotational microwave spectra: ∆j = ±1. this came from angular momentum conservation (a photon has spin angular momentum ħ). in raman scattering, one photon comes in and one photon goes out. what are the selection rules for rotational raman transitions? (a) δj = ±1
(b) δj = 0, ±1, ±2
(c) δj = 0, ±2 *
(d) δj = 0
this is because a photon comes in and transfers one unit of ħ to the molecule, and one photon comes out again, which again has one unit of ħ. if the incoming and outgoing photons have the same spin, δj = 0. if they have opposite spins, δj = ±2.

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