Please be more specific:
1. what do you mean with "Calculate"
2. fluorescence is from the vibrationless excited electronic state. So what vibrational mode do you mean?
Peter
The FC factors only apply when the (equilibrium) distance of the atoms in the molecule differs in ground and electronic state. The reason is that in this case the vibrational part of the transition moment does have a non-zero integral because of the equilibrium displacement. you can find quite a good description in Wikipedia under the heading Franck-Condon; explained there for a diatomic molecule for which the equilibrium distance has in general the largest displacement
Peter
Not all bond distances change and in that case there is no Franck-Condon flag in emission: please remember the questioner asks about CALCULATION of the vibrational MODES in fluorescence. Can you then give an answer to that?
Thank you very much Harry ten Br and Peter Kapusta for your responses,
First, I am new in this area, and my question came from my attempts to get the fluorescence spectrum with ADF code and with the help of ADF user Guid:
http://www.scm.com/Doc/Doc2014/ADF/ADFUsersGuide/page172.html
As the user Guid said I need to folow the instructions below to obtain the fluorescence spectrum::
First one needs to a the ground state geometry optimization, followed by a frequency calculation,
Next one needs to do an excited state geometry optimization, followed by a frequency calculation. Here it is assumed that the lowest singlet excited state S 1 is of interest,
“Next for the absorption spectrum, we look at excitations from the lowest vibrational state of the electronic ground state to the vibrational levels of the first singlet excited state S 1 (S 1 ← S 0 ), using the FCF program, which calculates the Franck-Condon factors between the vibrational modes of the two electronic states.
So:
1. The calculation of of the vibrational modes is in the optilized ground and excited geometry and it is not in the fluorescence,
2. “The FC factors only apply when the (equilibrium) distance of the atoms in the molecule differs in ground and electronic state”, and that what would hepened in fluorescence.
3. I asked this question because I thought that I do not need the the last step to get the fluorescence spectrum, the answer came from the ADF developer :” If you want the vibrationally resolved fluorescence spectrum you need to calculate the vibrational modes of the excited state and the vibrational modes of the ground state » Which means that I do not need to calculate these factors to obtained the fluorescence spectrum.
thanks a lot
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