Gas-phase C60Hn+q (n = 0–4, q = 0,1) fullerenes and fulleranes: spectroscopic simulations shed light on cosmic molecular structures

Abstract

The discovery of C₆₀, C₆₀⁺, and C₇₀ in the interstellar medium has ignited a profound interest in the astrochemistry of fullerene and related systems. In particular, the presence of diffuse interstellar bands and their association with C₆₀⁺ has led to the hypothesis that hydrogenated derivatives, known as fulleranes, may also exist in the interstellar medium and contribute to these bands. In this study, we systematically investigated the structural and spectroscopic properties of C₆₀H_n^+q (n = 0–4, q = 0,1) using an automated global minimum search and density functional theory calculations. Our results revealed novel global minimum structures for C₆₀H₂ and C₆₀H₄, distinct from previous reports. Notably, all hydrogenated fullerenes exhibited lower ionization potentials and higher proton affinities compared to C₆₀. From an astrochemical perspective, our results exposed the challenges in establishing definitive spectroscopic criteria for detecting fulleranes using mid-infrared and UV-Vis spectroscopies. However, we successfully identified distinct electronic transitions in the near-infrared range that serve as distinctive signatures of cationic fulleranes. We strongly advocate for further high-resolution experimental studies to fully explore the potential of these transitions for the interstellar detection of fulleranes.