2017ApJ...845...76Z

The recent detection of fullerene (C₆₀) in space and the positive assignment of five diffuse interstellar bands to C₆₀⁺ 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, C₆₀H_m, m = 1-60) may be abundant in space. In this paper, we present theoretical studies of the vibrational modes of isomers of C₆₀H_m. 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 µm 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.