THEORETICAL-STUDY OF POSSIBLE INTERSTELLAR PROCESSES FOR THE PRODUCTION OF C2CL PRECURSORS

An ab initio study of the reactions of C2H+ with hydrogen chloride and of Cl+ with acetylene has been carried out. Both reactions take place on the triplet (C2H2Cl)(+) surface. For the first reaction, C2H+ + HC l, the only exothermic products are HCCCl+ + H (33 kcal mol(-1)), and there is a barrier-free mechanism which implies formation of the inter mediate HCCClH+. In the case of the reaction of Cl+ + C2H2 production of HCCCl+ is also exothermic (18 kcal mol(-1)), but charge transfer is a competitive process, with a reaction enthalpy of -28 kcal mol(-1). Both processes are barrier-free but charge transfer should also be kin etically favored. Therefore, it seems that C2H+ + HCl could be a sourc e of HCCCl+, a precursor of C2Cl through dissociative recombination, w hereas the role of the reaction Cl+ + C2H2 should be severely limited. (C) 1998 Elsevier Science B.V.