THE VISIBLE EMISSION AND ABSORPTION-SPECTRUM OF C-60

The fluorescence spectrum of C-60 in Ne and Ar matrices is revisited i n the light of improved calculations of vibronically induced intensiti es for the transitions between S-0 and the lowest three singlet excite d states. The Jahn-Teller and Franck-Condon vibronic activities for th e three transitions are also evaluated and combined with the computed Herzberg-Teller intensities to simulate the fluorescence spectra. The agreement between experimental and simulated spectra is very satisfact ory and provides an assignment for almost every observed band. The exc itation spectrum of C-60 in Ne and Ar matrices in the 640-500 nm regio n is also presented. It is almost a mirror image to the fluorescence s pectrum of C-60 in Ar matrices and nearly all bands can be attributed by analogy with the fluorescence spectrum. However, it appears that so me mode frequencies increase while others decrease as compared to the fluorescence spectrum. In the high-frequency region evidence for a num ber of bands whose intensity has no counterpart in the fluorescence sp ectrum shows that they correspond to a(g)(2) overtones of bands appear ing at lower frequency. Finally a band is found which is attributed to Herzberg-Teller modes of a higher electronic state of T-2u symmetry. Its electronic origin is estimated to lie at similar to 16 700 cm(-1). (C) 1997 American Institute of Physics.