Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Normal mode

  1. Oct 20, 2013 #1
    What does one mean by normal mode of an object? Why is it 3n-5 for linear particles, 3n-6 for non linear particle where n is the number of particle.
  2. jcsd
  3. Oct 20, 2013 #2
    A normal mode is a specific type of vibration that a molecule can exhibit. They are "normal" because each type of vibration is distinct and cannot be replicated by any combination of the other types. Any possible type of vibration that a molecule can exhibit is just a combination of its normal modes.

    The numbers can probably be derived from symmetry arguments, I don't know how, but it's easier just to draw out molecules for n = 2 and 3 and try to convince yourself that there is an agreement with the formulas.
  4. Oct 20, 2013 #3
    Is there any book which explained it in more detailed manner! That you could recommend?
  5. Oct 20, 2013 #4
    There are loads, Bernath (2005) is pretty good for a conceptual overview in the context of spectroscopy, should be in most scientific libraries. But if you're serious about molecular spectroscopy.... Penner or Herzberg are solid, detailed (if a little old) texts.
  6. Oct 20, 2013 #5
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook