Possible Hydrocarbon Chemical Growth Routes from l-C3H+ in Dense Molecular Clouds

Abstract

The C₃H⁺ cation plays a pivotal role within the chemical network of dense interstellar clouds. Its relatively slow reaction with molecular hydrogen (H₂) suggests that reactions with other species, particularly small hydrocarbons, may play a significant role. In this study, we measured the absolute reaction cross sections of C₃H⁺ with acetylene (C₂H₂) and the two isomers of C₃H₄ (allene and propyne). To facilitate the implementation of our experimental data into astrochemical models, we converted the reaction cross sections into rate constants. No temperature dependency was observed for all of the investigated channels. The reaction rates for C₃H⁺ with C₂H₂ and C₃H₄, yielding C₅H₂⁺ and C₄H₃⁺, respectively, are in good agreement with existing data. However, we report a previously unidentified channel in the reaction with C₃H₄, leading to protonated acetylene C₂H₃⁺ with a 30% yield compared to the major product, C₄H₃⁺.