An “exact model” study of vibronic interactions in radiationless transitions with applications to internal conversion in pyrazine

Abstract

An “exact model” study of vibronic interactions and the “proximity effect” in radiationless transitions is reported. A comparison is made between the “exact” results and those obtained employing the crude adiabatic Born—Oppenheimer scheme and the adiabatic Born—Oppenheimer scheme. It is shown that the computed radiationless decay rates are very sensitive to the scheme adopted. The exact solutions of the linear Herzberg—Teller vibronic coupling model are employed in a theoretical investigation of the “proximity effect” and internal conversion in pyrazine. The presented results suggest that the deuterium isotope effect on the internal conversion rate in pyrazine may be very small, although the vibrational energy distribution in S 0 may be dramatically altered.