Mr./Miss/Mrs Bagheri, please read the discussion of the following question in 'ResearchGate':

'How can I convert epsilon to transmission or absorbance in IR spectra from Gaussian09 to compare with experimental IR spectra?'

I should ask, whether you need absorption or emission spectrum. The question is valid because the simplest, and usually applied method is to project geometry differences between the excited and ground state onto the normal modes of the final (!!!) state in the electronic transition.

The projection gives you the Franck-Condon parameters Bi (i denotes normal modes), which taken as Bi^2/2 are called Hunag-Rhys factors. Each HR factor governs the intensities of the vibronic lines in the Franck-Condon progression. The sum of ovelapping bands of the FC progressions give you the vibronically resolved spectrum. Tha actual shape you can get by representing each vibronic line by a gaussian or lorenzian function with specified width.

This is normally done by onw software that is rather easy to write. You can also obtain the FC parameters using the Dushin program of prof. Reimers (easy to google :).

Good luck!

Marcin Andrzejak

thanks Dear Marcin

thanks Dear Bojidarka