Vibronic Intensity Distribution in the Phosphorescence of Benzene and Its Deuterated Isomers

Abstract

The gound‐state vibrational frequencies and the relative vibronic intensities of the phosphorescence are calculated for all and measured for one carbon‐13 and ten of the possible twelve deuterium‐substituted benzenes. The intensities are calculated within the framework of the Herzberg–Teller model. It is shown that the relative intensities for different vibronic transitions of isotopically related molecules can be expressed in terms of two factors; a normal coordinate eigenvector matrix element which is isotope dependent, and an electronic term which is isotope independent. The observed C₆H₆ intensities are used to evaluate the electronic parameters. Excellent agreement is found among the calculated and observed intensities and frequencies. The relative importance of the different coordinates for vibronic coupling in benzene is indicated.