Example: Franck-Condon factors between ground and excited terms in ZnI molecule

Franck-Condon factors determine the probability of transitions between vibrational energy levels of different electronic terms in a molecule. They are equal to the squared integral of the product of the initial and final wave functions of the corresponding vibrational states belonging to different electronic terms.

Figures below demonstrate Franck-Condon factors calculated using vibrational wave-functions obtained within the Morse model and its quasi-classical approximation in the case of the high vibrational number. The parameters necessary for determining Morse quantum-mechanical wavefunctions of different electronic terms were obtained using quantum-chemical calculations.