Sorry.. I hit return too soon...
A more sophisticated answer might add some of the following:
The process where a photon is absorbed and a phonon is emitted is actually forbidden by angular momentum conservation -- photons have spin and phonons don't so you can't do this in a simple way. So in fact any scattering process that involves phonons and photons is a bit more complicated --- usually involving a photon scattering (having k_in and k_out) and a phonon being emitted. Nonetheless, because even a tiny change in k for the light ends up with a huge change in energy (because c is large), you still expect to only be able to interact with optical phonons -- those with k near zero, but omega nonzero.