The visible emission and absorption spectrum of C60

The fluorescence spectrum of ${\mathrm{C}}_{\mathrm{60}}$ in Ne and Ar matrices is revisited in the light of improved calculations of vibronically induced intensities for the transitions between $S_0$ and the lowest three singlet excited states. The Jahn–Teller and Franck–Condon vibronic activities for the 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 satisfactory and provides an assignment for almost every observed band. The excitation spectrum of ${\mathrm{C}}_{\mathrm{60}}$ in Ne and Ar matrices in the 640–500 nm region is also presented. It is almost a mirror image to the fluorescence spectrum of ${\mathrm{C}}_{\mathrm{60}}$ in Ar matrices and nearly all bands can be attributed by analogy with the fluorescence spectrum. However, it appears that some mode frequencies increase while others decrease as compared to the fluorescence spectrum. In the high-frequency region evidence for a number of bands whose intensity has no counterpart in the fluorescence spectrum shows that they correspond to $a_g\text{(2)}$ overtones of bands appearing at lower frequency. Finally a band is found which is attributed to Herzberg–Teller modes of a higher electronic state of $T_{\text{2u}}$ symmetry. Its electronic origin is estimated to lie at $\text{∼16\hspace{0.17em}700\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}}.$