Reactions of Acetonitrile with Trapped, Translationally Cold Acetylene Cations.

The reaction of the acetylene cation (C 2 H 2 + ) with acetonitrile (CH 3 CN) is measured in a linear Paul ion trap coupled to a time-of-flight mass spectrometer. C 2 H 2 + and CH 3 CN are both noted for their astrochemical abundance and predicted relevance for understanding prebiotic chemistry. The observed primary products are c -C 3 H 3 + , C 3 H 4 + , and C 2 NH 3 + . The latter two products react with excess CH 3 CN to form the secondary product C 2 NH 4 + , 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 C 2 NH 3 + , two isomers of C 3 H 4 + , and the cyclopropenyl cation c -C 3 H 3 + . 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.