The (n, π∗) absorption spectrum of benzophenone. A new model for the excited state dynamics

We present a new model for the excited state dynamics and S1 ← S0 (n, π∗) absorption spectrum of benzophenone. As part of this model, we present compelling evidence for the activity of a symmetric bending mode (ν62) with frequency of approximately 140 cm−1 in the excited state. This result contrasts with previous work based on models in which the second low-frequency mode is the asymmetric twist whose activity is due to coupling with the symmetric twist. We analyze the effects of deuterium and fluorine substituents, and show how the results could be used to test the identity of the optically active modes.