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(long) question - Raman, IR spectroscopy; virtual energy states, light; heat

  1. Jun 17, 2011 #1
    I'm confused about what is going on theoretically with Raman, and light in general, wrt photon absorption, annihilation, and re-emission; I don't have the math background to understand Fourier transform, of anything past simple algebra anymore, but would like to at least have a decent qualitative understanding.

    1. I don't understand what is meant by "virtual" energy states.

    2. I’m also confused with the difference between an electron needing a photon of a specific energy to move to a higher quantum level, and then re-emitting a new photon as it de-excites to a lower n-level, vs if a photon entering a Raman spectrometer is absorbed that there are some other kind of energy states that are not coming from quantum levels for electrons ('virtual'?), yet the atoms are emitting energies in the form of photons - it's not making sense for me that these photons are not coming from a de-exciting electron making a quantum jump down, that is, they are emitting photons of say IR but these aren’t coming from a specific quantum leap down from one n-level to another (?)

    3. Another thing that I'm having trouble understanding, related but different, is how IR photons can be described also as heat - something is lost here on me - I think of heat as a transfer of vibrational motion on the atomic level - how is infrared radiation also “heat”, per se? How does heat, or say a photon of IR frequency, "heat" something up - or also, if something is emitting IR photons, is that energy coming from de-excitation of electrons from the object's atoms as they fall back to ground state? (Perhaps there are different definitions of ‘heat’ and I need that cleared up.)

    Can photons be emitted from different aspects of an atom, or rather, groups of atoms, and not just from electron quantum transitions? Am I confusing different sources of energy transfer - ie, photon absorption vs. say electrical transfer of energy? If a CCD is detecting a photon, which can also be described as a wave, what are the possible sources or originations of that photon ?

    I also don’t understand yet fluorescence and how that works with getting in the way of Raman emission.

    The word "scattering" I'm guessing means that photons are scattered, but the source of these photons I don't understand, and again, virtual energy states that arise from inelastic scattering - what is that - are these energy states unrelated to electron quantum transitions, that come from phonon vibrations/polarizations? I think I'm hung up on thinking that all photons must come from electrons in atoms being emitted after absorbing photons from another source.

    I seem to think that if a photon say of IR is emitted from a depolarizing chunk of matter, that IR photon has to have enough energy to collide with an electron in an atom say in a CCD which moves that electron to another quantum state, etc.

    I seem to have forgotten also how IR spectroscopy really works, as well, qualitatively - is this also virtual (whatever that means) transition emission?

    Thanks in advance for any info anyone can help enlighten me with, -Jackson. oreilly.jackson@gmail.com
  2. jcsd
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