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Raman spectroscopy

  1. Aug 7, 2005 #1
    raman spectroscopy!!!

    Hi, can anybody please tell what is the speciality of Raman spectroscopy and how it differs from other techniques?? does it have any uniqueness? more info is welcomed! thanks in advance.
    Last edited: Aug 7, 2005
  2. jcsd
  3. Aug 7, 2005 #2
  4. Aug 7, 2005 #3

    Claude Bile

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    Raman spectroscopy excites transitions forbidden by infrared spectroscopy as Raman transitions are bound by different selection rules.

  5. Aug 8, 2005 #4
    I am not sure i get your point here. What are you talking about ? Could you clarify, please ?

    I am no specialist on this but doesn't IR spectroscopy involve electronic energy transitions induced by the incoming IR photon, while Raman spectroscopy is just the phonon transitions induced by the scattering of a photon at the lattice-atoms ? By this scattering process, a phonon is either emitted or absorbed : ie the Stokes and anti-Stokes lines ?

  6. Aug 8, 2005 #5
    Raman scattering and IR speoectroscopy compliment each other when we are dealing with molecules having centre of inversion symmetry. In these molecules raman active lines are forbidden in IR and vice versa. Coming to vibrational and rotational lines in a spectrum..vibrations are obsorved in infra-red region and rotations in microwave region,,but when we look at the pure vibrational spectra we can also see rotational lines which should not be there as they belong to microwave region..why does this happen?
  7. Aug 8, 2005 #6

    Claude Bile

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    Marlon, infrared spectroscopy excites vibrational energy states in a given molecule (although there are electronic transitions that are excited by infrared wavelengths, the term infrared spectroscopy usually refers to vibrational transitions. The more correct name for infrared spectroscopy is vibrational or rovibrational spectroscopy).

    A vibrational state is excited through infrared spectroscopy if there is a variation in the dipole moment of the molecule as the molecule vibrates. Some vibrations (such as symmetric vibrations) are not infrared active because their dipole moment is constant.

    A vibrational state is excited through Raman spectroscopy if there is a variation in the polarisability of the molecule.

    Photon79, you are not allowed to double post in these forums, I'm pretty sure marlon already warned you once before. Read my response on the other thread and if you have further questions, post them there.

    Last edited: Aug 8, 2005
  8. Aug 9, 2005 #7
    Thanks Claude for the explanation. I also looked it up on Wikipedia, and i do realize where i was wrong.

    Thanks again

  9. Aug 9, 2005 #8

    Claude Bile

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    Not a problem Marlon, :smile: .

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