The visible emission and absorption spectrum of C60

Abstract

The fluorescence spectrum of C60 in Ne and Ar matrices is revisited in the light of improved calculations of vibronically induced intensities for the transitions between S0 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 C60 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 C60 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 ag(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 T2u symmetry. Its electronic origin is estimated to lie at ∼16 700 cm−1.

Interstellar fullerene compounds and diffuse interstellar bands

“…However, Herzberg-Teller coupling with vibrational states (plus complex Jahn-Teller effect, Chancey & O'Brien 1997) allows spectacular weak absorption and fluorescence emission in the forbidden transitions from the first singlet excited states; however, its very rich energy structure is extremely difficult to disentangle (Sassara et al 1997;Orlandi & Negri 2002;Cavar et al 2005), see Appendix E.…”

“…Schematic diagram of basic electronic shells of C 60 in Hückel approximation and resulting first excited states of C 60 (E <∼ 3 eV), singlet (see e.g. Sassara et al 1997Sassara et al , 2001) and triplet. b) From Table 6 of Bendale et al (1992).…”

Vibrational spectroscopy of C60

“…The first assignment, favored by Schettino et al [72], is in better agreement with first-principles calculations and is consistent with a weak peak observed at 714 cm −1 in fluorescence experiments [80,108]. However, the close proximity of the H g (3) mode at 709 cm −1 makes it difficult to reach definitive spectroscopic conclusions.…”

“…Copley et al [78] find an INS peak at 970 cm −1 which has a total integrated intensity consistent with these three modes. The frequency of the G u (4) mode is 961 cm −1 according to the fluorescence experiments [80,108]. We obtain an excellent fit of the INS data of [78] by further assuming that the frequencies of the T 2u (3) and A u modes are 973 cm −1 and 984 cm −1 , respectively.…”

“…The Jahn-Teller contribution is dominated by Ramanactive H g modes and therefore offers little additional insight into the vibrational structure of C 60 . However, this contribution must be computed for a detailed quantitative comparison between experimental and theoretical fluorescence spectra, as recently done by Sassara et al [108]. They also included Franck-Condon terms and extended the calculations to take into account two additional many-electron excited states, of t 3u and h g symmetry.…”