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

Frank-Condon Principle - Potential Energy Surfaces

Tags:
  1. Nov 7, 2014 #1
    Theory and my Understanding:

    So I understand how the frank condon principle lets us effect electronic transitions instantaneously, since the motion of nuclei (on the timescale of such electronic transitions) is quite slow.

    Consequently, when a photon of light is absorbed you can have an electron being promoted from the Sx0 to the Sy1 where S represents the singlet state and x and y are vibrational levels (x>y)

    My Question

    What effects how much the upper curve is translated over to the right-hand-side, with respect, to the lower curve ?

    My Interpretation

    When an electron is promoted from S00 to S21, for example, the electron is being put into an anti-bonding orbital consequently weakening bonds and leading to a greater vibrations.

    The more anti-bonding character the S1 state has the greater the amount by which the upper curve is translated over to the right-hand-side and hence the larger the vibrations.

    9XrmEfW.jpg
     
  2. jcsd
  3. Nov 8, 2014 #2

    DrDu

    User Avatar
    Science Advisor

    Yes, your explanation sounds good.
     
  4. Nov 8, 2014 #3
    Thanks! I just have one last question, if you imagine a porphyrin ring versus simple benzene. It is my belief that the upper curve (see above diagram) is displaced more to the right in benzene.

    This is because a single electronic excitation in a massive porphyrin ring (a multi electron system) is unlikely to change the bonding character of the molecule by that much.
     
  5. Nov 8, 2014 #4

    DrDu

    User Avatar
    Science Advisor

    Yes, but it depends on the localization of the orbitals that are involved.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Frank-Condon Principle - Potential Energy Surfaces
  1. Frank Condon Blockade (Replies: 1)

Loading...