Out-of-plane vibrations in T(n pi*) -> S-0 of benzaldehyde

The phosphorescence spectra of benzaldehyde and benzaldehyde-d(1) in a benzene polycrystalline matrix at 4.2 degrees K reveal that a non-totally symmetric vibration associated with the out-of-plane aldehyde hydrogen wag is active. This observation establishes the importance of out-of-plane vibronie coupling in T(n pi*) -> S-0. The importance of the out-of-plane vibration is attributed to vibronic coupling between T(n pi*) and T(pi pi*). The proximity of the matter state to S(n pi*) leads to unusually effective spin-orbit coupling with that state.