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Homework Help: Get vibration frequency form absorption spectra line

  1. Apr 19, 2017 #1
    1. The problem statement, all variables and given/known data

    "Absorption spectra of gaeous HCl show a line at 3.5 μm which results form molecular vibration (oscillation from interatomic distance)" How do I get the frequency of vibration from this?

    2. Relevant equations

    ? If I knew this, then I could probably solve the problem

    3. The attempt at a solution

    Is the wavelength 3.5μm? I don't see a relevant explanation in my book (An Introduction to Thermal Physics).
  2. jcsd
  3. Apr 19, 2017 #2


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    Science Advisor

    Yes, the fact that the absorption line is at 3.5 μm means that the wavelength of the absorbed radiation is 3.5 μm. The question asks what frequency is this radiation.
  4. Apr 19, 2017 #3
    OK, thanks.

    Also, I'm unsure about the last part of this question - to approximately what temperature would the gas have to be heated to excite vibrations thermally? Again, I feel like there is just some equation or basic fact that I should know to solve this, but it isn't clear to me what that would be.
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