A quantum study of the chemical formation of cyano anions in inner cores and diffuse regions of interstellar molecular clouds

Abstract

The barrierless, exothermic reactions of H- with HCnN cyanopolyynes, with n = 1 and 3, are analyzed using ab initio calculations of the interaction forces. The shape of the reactive potential energy surface suggests the most efficient approach of H- to be on a nearly collinear arrangement on the H-side of HCnN. Using simple transition state formulation of the reaction rates, which are obtained via calculation of the partition functions of each transition state configuration, provides a new non-Langevin behavior of the reaction which can help explain the unexpectedly large density of CN- formation found in observations. A similar procedure is also employed for the reaction of H- with HC3N and the differences in the results, indicating a lower efficiency of the latter reactivity compared with that for CN-, are discussed in this paper.