Raman Spectroscopy Lecture: Stokes, Anti-Stokes, and Rayleigh Scattering

In this lecture I describe the difference between conventional IR spectroscopy and Raman Spectroscopy. I also discuss what Raman spectra look like and explain Stokes, Anti-Stokes, and Rayleigh scattering processes.
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[@llucasdoria]

Hi Professor Melko, one more question from me here: If I got this straight, even that O2 doesn't absorb IR light, it still interacts with it in the form of scattering. So can I say that the O2 is "emitting" IR? Said differently, I'm not quite sure how to appoint the fact that O2 has vibrational transitions due to IR light. If I can't say it "emits" IR, how can I characterize the light that comes out of the scattering with O2 into a detector for example?
Great lecture. Thanks a lot!!

[@ProfMelko]

I guess this is somewhat just a matter of vocabulary. Remember that sometimes it is useful to think about light as a photon (for absorption and emission) but other times it is useful to think of it as a wave, and really it has properties of both and is an entity that is not characterized completely one way or the other. In Raman, I think of the electrons "responding" to a light wave that is passing by in real time, not as a direct absorption that imparts momentum directly on the electron (even this is thinking of the electron as a particle, when it too is a particle AND wave). So while I guess you could think of Raman as absorption event followed by instantaneous emission, it would have to occur with zero time loss, so a simultaneous absorption and emission, but that doesn't really make sense to me. I picture it as the electron responding in real-time to a passing photon or electric field, kind of like a person on a raft will bob up and down when a boat passes by.