Non-condon scheme of radiationless transitions for the morse oscillator model

The non-adiabatic coupling matrix elements responsible for radiationless deactivation of an electronically excited molecule are calculated without invoking the Condon approximation. Assuming the Morse potential surfaces for vibrational motion along the local and totally symmetric normal coordinates, the vibronic part of the radiationless rate constant is calculated. It is shown that the rate constant in the non-Condon scheme exceeds that obtained in the Condon approximation by about two orders of magnitude. The calculated dependence of the radiationless rate constant on the energy gap is in good agreement with the experimentally observed energy gap law for intersystem crossing T₁ → S₀ rate constants in aromatic hydrocarbons.