Discussion
The selection rules for vibrational Raman spectra and rotational Raman spectra are :
Answer: C
The rules are Δν = ±1 and ΔJ = 0, ±2 respectively.
Raman scattering involves two photons, so it follows the polarisability rather than the dipole moment. For a harmonic vibration the polarisability changes linearly with displacement, giving Δv = ±1 (Stokes and anti-Stokes lines). For rotation of a linear molecule the polarisability repeats twice per turn, giving ΔJ = 0, ±2; ΔJ = 0 is the unshifted Rayleigh line.
ΔJ = 0, ±1 is the rule for infrared rotation-vibration spectra, and including Δv = 0 in the vibrational rule only adds the Rayleigh line, not a vibrational Raman line.
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