Vibronic coupling and polyatomic spectra

A theoretical account of the vibronic intensity borrowing in polyatomic spectra is described and applied to the 3200 Å n → π^* absorption of pyrazine and the 3700 Å π → π^* absorption of pyrene. It is shown that the asymmetry between absorption and emission, as well as the frequency of the inducing mode in the lowest excited singlet state, are correctly predicted for both of these systems.