Theoretical Study of the Reaction of HCl with C3H2+: A Possible Source of Carbon−Chlorine Compounds in Space

Abstract

A theoretical study of the (ClC 3 H 3 ) + species has been carried out. Two different models, G2 and QCISD(T) at the B3LYP geometries, have been employed. Our calculations predict that the global minimum is an open-chain isomer ClHCCCH 2 +( 2 A), whereas five different open-chain structures are also quite stable, lying about 5.9-13.1 kcal/mol above the ground state. The lowest-lying cyclic isomer, with a three-membered carbon ring, lies about 18.3 kcal/mol higher in energy. These theoretical results allow the development of thermodynamic arguments about the reaction pathways of the process HCI + C 3 H 2 +. For the reaction of HCl with CCCH 2 +, formation of different chlorine-carbon compounds is exothermic and there are several mechanisms leading to these species that are barrier-free. However, production of carbocation compounds (cyclopropenyl cation, c-C 3 H 3 +, and propargyl cation, l-C 3 H 3 +) could be competitive with the formation of chlorine-carbon species. The predicted dominant channels for the reaction with both HCCCH + and c-C 3 H 2 + isomers are l-C 3 H 3 + and c-C 3 H 3 +, respectively. Therefore, only the reaction of HCl with the CCCH 2 + isomer seems to be a possible source of chlorine-carbon compounds in space.