Infrared spectra of protonated and deuteronated C\(_{{60}}\) in interstellar environments

Abstract

With the credible detection of C\(_{60}\), C\(_{70}\) and C\(_{70}^+\) in the interstellar medium (ISM), new prospects have opened up for the search of other fullerenes and their derivatives. Since fullerenes show high proton affinities, their protonated forms should predominate in the ISM, which can easily go through deuterium enrichment. Here, we present the infrared (IR) spectra and standard enthalpy of formation of C\(_{60}\)H\(^{+}\), C\(_{60}\)D\(^{+}\), C\(_{60}\)H\(_{18}^{+}\) and C\(_{60}\)D\(_{18}^{+}\) using Density Functional Theory (DFT) in singly ionized forms. The obtained computed IR spectra are compared with the observations. The results show that the four mid-infrared bands of neutral C\(_{60}\) are still visible in C\(_{60}\)H\(^{+}\) and C\(_{60}\)D\(^{+}\), but their strength diminishes in C\(_{60}\)H\(_{18}^{+}\) and C\(_{60}\)D\(_{18}^{+}\). As a conclusion, it is possible that the IR bands ascribed to C\(_{60}\) are a mixture of pure and slightly protonated and deuteronated fullerenes. In this way, the observed scattering of the C\(_{60}\) band ratios could be explained.