Quantum-Chemical Modeling and Analysis of the Vibrational Structure in the Phosphorescence Spectrum of C60

Abstract

The phosphorescence spectrum of C60, recently obtained in alkane and in Xe matrixes at low temperature, has been modeled by means of semiempirical quantum chemical calculations. The T1 → S0 transition in the unperturbed molecule is symmetry as well as spin multiplicity forbidden. The intensities of the false origins due to inducing modes have been calculated in terms of the Herzberg−Teller mechanism combined with an expansion over spin−orbit perturbations. To date, this is the first modeling of the phosphorescence spectrum of C60 entirely based on computed molecular parameters. Thus, the analysis of the spectrum is based not only on vibrational frequencies, but also on the comparison between computed and observed vibronic intensities. The calculations indicate that the vibrational structure is dominated by false origins due to modes of hu, gu, and t1u symmetry, but contains also a number of combination bands based mainly on the Jahn−Teller active hg(1) mode.