= Solution
The gross requirement is \b[an anisotropic <polarizability tensor>], so that changing molecular orientation changes the induced response. A permanent <electric dipole moment> is not required; a homonuclear diatomic can therefore have a rotational <Raman scattering> spectrum.
For the inelastic lines of a linear <rigid rotor>, the detailed rule is \b[$\Delta J=\pm2$], with $J\geq0$. The $\Delta J=0$ contribution is unshifted <Rayleigh scattering>, not a rotational <Stokes Raman scattering> line. <Stokes Raman scattering> has $\Delta J=+2$ because the molecule gains rotational <energy>.
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