A theoretical study of the (ClC3H3)(+) 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 CIHCCCH2' (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 HCl+ C3H2+. For the reaction of HCl with CCCH2+, 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-C3H3+, and propargyl cation, l-C3H3+) could be competitive with the formation of chlorine-carbon species. The predicted dominant channels for the reaction with both HCCCH+ and C-C3H2+ isomers are l-C3H3+ and C-C3H3, respectively. Therefore, only the reaction of HCL with the CCCH2+ isomer seems to be a possible source of chlorine-carbon compounds in space.