A model for the hydrogenation and charge states of fullerene C₆₀

Implications for diffuse interstellar band research

¹ Laboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
e-mail: abbink@strw.leidenuniv.nl
² LUNEX EuroMoonMars EuroSpaceHub, SBIC Space Business Innovation Centre, Kapteynstraat 1, 2201 BB Noordwijk, The Netherlands

Received: 16 July 2023
Accepted: 4 January 2024

Abstract

Context. The diffuse interstellar bands (DIBs) are a set of ∼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 C₆₀⁺.

Aims. This work aims to narrow down which compounds related to C₆₀ 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⁺.