Laboratory confirmation of C₆₀⁺ as the carrier of two diffuse interstellar bands

Abstract

The diffuse interstellar bands are absorption lines seen towards reddened stars¹. None of the molecules responsible for these bands have been conclusively identified². Two bands at 9,632 ångströms and 9,577 ångströms were reported in 1994, and were suggested to arise from C₆₀⁺ molecules (ref. 3), on the basis of the proximity of these wavelengths to the absorption bands of C₆₀⁺ measured in a neon matrix⁴. Confirmation of this assignment requires the gas-phase spectrum of C₆₀⁺. Here we report laboratory spectroscopy of C₆₀⁺ in the gas phase, cooled to 5.8 kelvin. The absorption spectrum has maxima at 9,632.7 ± 0.1 ångströms and 9,577.5 ± 0.1 ångströms, and the full widths at half-maximum of these bands are 2.2 ± 0.2 ångströms and 2.5 ± 0.2 ångströms, respectively. We conclude that we have positively identified the diffuse interstellar bands at 9,632 ångströms and 9,577 ångströms as arising from C₆₀⁺ in the interstellar medium.