Search for Hydrogenated C 60 (Fulleranes) in Circumstellar Envelopes

Abstract

The recent detection of fullerene (C 60 ) 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 C 60 can be readily hydrogenated, raising the possibility that hydrogenated fullerenes (or fulleranes, C 60 H m , m  = 1–60) may be abundant in space. In this paper, we present theoretical studies of the vibrational modes of isomers of C 60 H m . Our results show that the four mid-infrared bands from the C 60 skeletal vibrations remain prominent in slightly hydrogenated C 60 , but their strengths diminish in different degrees with increasing hydrogenation. It is therefore possible that the observed infrared bands assigned to C 60 could be due to a mixture of fullerenes and fulleranes. This provides a potential explanation for the observed scatter of the C 60 band ratios. Our calculations suggest that a feature around 15 μ m due to the breathing mode of heavily hydrogenated C 60 may be detectable astronomically. A preliminary search for this feature in 35 C 60 sources is reported.