Reactions of Acetonitrile with Trapped, Translationally Cold Acetylene Cations

The reaction of the acetylene cation (C2H2 +) with acetonitrile (CH3CN) is measured in a linear Paul ion trap coupled to a time-of-flight mass spectrometer. C2H2 + and CH3CN are both noted for their astrochemical abundance and predicted relevance for understanding prebiotic chemistry. The observed primary products are c-C3H3 +, C3H4 +, and C2NH3 +. The latter two products react with excess CH3CN to form the secondary product C2NH4 +, protonated acetonitrile. The molecular formula of these ionic products can be verified with the aid of isotope substitution via deuteration of the reactants. Primary product reaction pathways and thermodynamics are investigated with quantum chemical calculations and demonstrate exothermic pathways to two isomers of C2NH3 +, two isomers of C3H4 +, and the cyclopropenyl cation c-C3H3 +. This study deepens our understanding of the dynamics and products of a pertinent ion–molecule reaction between two astrochemically abundant molecules in conditions that mimic those of the interstellar medium.