THE FULLERENE C60H2 AND THE INTERSTELLAR EXTINCTION

A measurement of the ultraviolet-visible absorption spectrum of C60H2, the dihydride of the soccer-ball molecule C60, is discussed in the context of the variable component of the interstellar extinction. The spectrum of C60H2 consists of a smooth continuum with a series of rounded peaks in the ultraviolet. The continuum resembles the extinction curve of the variable component in so far as both are weak in the red and strengthen monotonically towards shorter wavelengths, but the peaks are not seen in the extinction. There is a systematic smoothing of the spectrum in going from C60 to C60H2, with the peaks becoming weaker and the colour approaching that of the astronomical extinction, and, if these trends continue as more hydrogen atoms are added, it may be possible to account for the variable component in terms of the collective opacity of a population of interstellar fulleranes in which most of the molecules bear more than two hydrogen atoms.