A model for the hydrogenation and charge states of fullerene C60 Implications for diffuse interstellar band research

Context. The diffuse interstellar bands (DIBs) are a set of similar to 600 absorption features at optical and near-infrared wavelengths that are found in the interstellar medium in the Milky Way and other galaxies. They remain mostly unidentified and represent the greatest unsolved mystery in astronomical spectroscopy of the past 100 years. Many studies indicate that the carrier molecules are likely carbonaceous molecules, such as polycyclic aromatic hydrocarbons (PAHs) or fullerenes, a theory that is supported by the identifications of five DIBs in the near-infrared attributed to C-60(+). Aims. This work aims to narrow down which compounds related to C-60 could be promising DIB carrier candidates. We did so by conducting a theoretical study of its hydrogenation and charge balance. Methods. We defined a system of relevant reactions, and for each reaction we computed or derived from the literature a reaction rate coefficient. Assuming a steady state, we then computed a distribution of relative abundances in each hydrogenation and charge state. Results. From the model outcomes, we expect the most abundant hydrogenated buckminsterfullerene compound in the diffuse interstellar medium to be C60H+.