Absorption Wavelengths and Bandwidths for Interstellar Searches of C60in the 2400–4100 A Region

Low-temperature gas-phase wavelengths and bandwidths for astronomical searches for C 60 in the 2400-4100 Å region are determined from the absorption spectra of C 60 in rare gas matrices at 4 K, coupled with information on the dependence of the vibronic transition frequencies of this fullerene on the Lorentz-Lorenz polarizability parameter of matrices and solvents. These bandwidths increase from 25 ± 5 cm -1 for the 1 1 T 1 u -1 1 A g band at 4024.0 ± 0.5 Å to 2300 ± 200 cm -1 for the 6 1 T 1 u -1 1 A g band at 2488 ± 8 Å. Spectral observations of astrophysical objects considered to be likely sites of C 60 have been examined in the context of the wavelengths and bandwidths of bands of the allowed transitions of C 60 which we recommend for searches of this species. No certain positive assignment of a C 60 band has been made in the 2400-4100 Å spectral region of these objects. The physical origin of the observed C 60 absorption bandwidths is analyzed and discussed in an appendix.