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

The C 3 H + cation plays a pivotal role within the chemical network of dense interstellar clouds. Its relatively slow reaction with molecular hydrogen (H 2 ) 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 C 3 H + with acetylene (C 2 H 2 ) and the two isomers of C 3 H 4 (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 C 3 H + with C 2 H 2 and C 3 H 4, yielding C 5 H 2 + and C 4 H 3 +, respectively, are in good agreement with existing data. However, we report a previously unidentified channel in the reaction with C 3 H 4, leading to protonated acetylene C 2 H 3 + with a 30% yield compared to the major product, C 4 H 3 + .