Theoretical evaluation of the vibronic intensity distribution in the phosphorescence of benzene

The relative intensity of the vibronic components of the phosphorescence spectrum of benzene has been evaluated theoretically. All mechanisms that may be responsible for the intensity of the most prominent bands have been taken into account and the relevant spin—orbit and vibronic coupling matrix elements have been evaluated. In agreement with experimental findings, it is found that vibronic coupling in the triplet manifold plays the dominant role in inducing the e _2g bands and that the ν ₈ bands is the most intense. The b _2g bands appear to be weak because of substantial cancella occurring between large separate contributions. Our results indicate that consideration of all terms and of several intermediate excited states is nece to obtain a correct picture of phosphorescence of benzene.