Benzene formation on interstellar dust grain analogues via single-atom Fe catalysis

ABSTRACT Benzene has been detected across a range of astrophysical environments, though the primary mechanism underpinning its formation has not yet been constrained and the extreme conditions of the interstellar medium often necessitate the need for grain-surface mediated reactions. However, while interstellar grains are known to enhance encounter rates and dissipate energy from exothermic reactions, their potential as chemical catalysts remains less explored. Here, we present mechanistic insights into the formation of benzene through successive cyclotrimerization of space abundant acetylene under astrophysical conditions, using single-atom Fe-containing silica surfaces as interstellar heterogeneous catalysts. Periodic quantum chemical calculations were performed to identify stationary points and transition states to construct a reaction potential energy surface, whilst binding energy and transition state theory rate calculations were also performed to evaluate the catalytic efficiency and identify plausibility across a range of astrophysical environments. Our results identify a thermodynamically favourable exergonic processes with small activation energy barriers, offering a novel route that can explain the presence of benzene across diverse astrophysical regions where current models cannot reproduce observational quantities.