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

Laboratory measurements of the gas-phase spectrum of C 60 + confirm that the diffuse interstellar bands observed at 9,632 ångströms and 9,577 ångströms arise as a result of C 60 + in the interstellar medium. Fullerene C 60 identified in the Milky Way Lick Observatory astronomer Mary Lea Heger first observed what were to be called 'diffuse interstellar bands' in 1919. These are absorption lines seen towards reddened stars, and although hundreds are now known, until now none of the molecules giving rise to them have been conclusively identified. In 1994, Bernard Foing and Pascale Ehrenfreund reported two diffuse interstellar bands with wavelengths close to those of the absorption bands of fullerene C 60 + measured in a neon matrix. A more certain identification awaited the gas-phase spectrum of C 60 + . John P. Maier and colleagues now present laboratory measurements of the gas-phase spectrum of C 60 + and confirm that the diffuse interstellar bands that Foing and Ehrenfreund observed do arise from C 60 + . As C 60 has already been detected in various nebulae by detection of its infrared spectrum, this new observation in the Milky Way can only add to current interest in the role of astronomical fullerenes. The diffuse interstellar bands are absorption lines seen towards reddened stars 1 . None of the molecules responsible for these bands have been conclusively identified 2 . Two bands at 9,632 ångströms and 9,577 ångströms were reported in 1994, and were suggested to arise from C 60 + molecules (ref. 3 ), on the basis of the proximity of these wavelengths to the absorption bands of C 60 + measured in a neon matrix 4 . Confirmation of this assignment requires the gas-phase spectrum of C 60 + . Here we report laboratory spectroscopy of C 60 + 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 C 60 + in the interstellar medium.