THEORETICAL-STUDY OF A BASIC PROCESS IN INTERSTELLAR CHLORINE CHEMISTRY - REACTION OF C+ WITH HCL

An ab initio study of the reaction of C+ with HCl has been carried out at two levels of correlated wave functions: MP2 and MCSCF + first-order CI. The reaction has been found to be exothermic by 53 kcal/mol, a value much lower than previous estimations from crossed-beam experiments. We have studied two different mechanisms for this process: direct hydrogen abstraction from the ion-molecule complex, CClH+, and isomerization of this complex into HCCl+ followed by subsequent hydrogen abstraction to give CCl+ + H. The transition states for both channels lie below reactants, and therefore both are possible interstellar processes. However, the respective energy barriers from CClH+ are very similar and consequently the two processes appear equally efficient from the energetic point of view. The present results which predict that HCCl+ is a strongly bound system suggest that the interpretation of crossed-beam experiments, from which it was deduced that the reaction intermediate was a weakly-bound species, should be revised.