Search for Hydrogenated C60 (Fulleranes) in Circumstellar Envelopes

The recent detection of fullerene (C60) in space and the positive assignment of five diffuse interstellar bands to reinforce the notion that fullerene-related compounds can be efficiently formed in circumstellar envelopes and be present in significant quantities in the interstellar medium. Experimental studies have shown that C60 can be readily hydrogenated, raising the possibility that hydrogenated fullerenes (or fulleranes, C60Hm, m = 1-60) may be abundant in space. In this paper, we present theoretical studies of the vibrational modes of isomers of C60Hm. Our results show that the four mid-infrared bands from the C60 skeletal vibrations remain prominent in slightly hydrogenated C60, but their strengths diminish in different degrees with increasing hydrogenation. It is therefore possible that the observed infrared bands assigned to C60 could be due to a mixture of fullerenes and fulleranes. This provides a potential explanation for the observed scatter of the C60 band ratios. Our calculations suggest that a feature around 15 m due to the breathing mode of heavily hydrogenated C60 may be detectable astronomically. A preliminary search for this feature in 35 C60 sources is reported.