Formation of different isotopomers of chloronium in the interstellar medium

Liton Majumdar, Ankan Das, Sandip K. Chakrabarti

Published 2014-01-05, updated 2014-01-10Version 2

Main focus of this paper is to explore the possibility of findings two deuterated isotopomers of H2Cl+ (Chloronium) in and around the Interstellar Medium (ISM). Presence of Chloronium ion has recently been confirmed by Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared (Neufeld et al., 2012). It observed para-chloronium towards six sources in the Galaxy. Existence of its deuterated isotopomers (HDCl+ & D2Cl+) are till date not discussed in the literature. We find that these deuterated gas phase ions could be destroyed by various ion-molecular reactions, dissociative recombination (DR) and by cosmic rays (CR). We compute all the Ion-molecular (polar) reaction rates by using the parameterized trajectory theory and the Ion-molecular (non-polar) reaction rates by using the Langevin theory. For DR and CR induced reactions, we adopt two well behaved rate formulas. We also include these rate coefficients into our large gas-grain chemical network to study the chemical evolution of these species around the outer edge of the cold dense cloud. In order to study spectral properties of chloronium ion and its two deuterated isotopomers, we have carried out quantum chemical simulations. We calculated ground state properties of these species by employing second order Moller-Plesset perturbation theory (MP2) along with quadruple-zeta correlation consistent (aug-cc-pVQZ) basis set. Infrared and electronic absorption spectra of these species are calculated by using the same level of theory. MP2/aug-cc-pVQZ level of theory is used to report the different spectroscopic constants of these gas phase species. These spectroscopic constants are essential to predict rotational transitions of these species. Our predicted column densities of D2Cl^+, HDCl^+ along with the spectral information may enable their future identification around outer edges of cold dark clouds.