Spectroscopic characteristics of the cyanomethyl anion and its deuterated derivatives

Abstract

It has long been suggested that CH2CN- might be a carrier of one of the many poorly characterized diffuse interstellar bands. In this paper, our aim is to study various forms of CH2CN in the interstellar medium. Aim of this paper is to predict spectroscopic characteristics of various forms of CH2CN and its deuterated derivatives. Moreover, we would like to model the interstellar chemistry for making predictions for the column densities of such species around dark cloud conditions. A detailed quantum chemical simulations to present the spectral properties of various forms of the CH2CN. MP2 theory along with the aug-CCPVTZ basis set is used to obtain different spectroscopic constants of CH2CN-, CHDCN- and CD2CN- in the gas phase which are essential to predict rotational spectra of these species. We performed quantum chemical calculation to find out energetically the most stable spin states for these species. We have computed IR and electronic absorption spectra for different forms of CH2CN. Moreover, we have also implemented a large gas-grain chemical network to predict the column densities of various forms of the cyanomethyl radical and its related species. In order to mimic physical conditions around a dense cloud region, the variation of the visual extinction parameters are considered with respect to the hydrogen number density of the simulated cloud. Our quantum chemical calculation reveals that the singlet spin state is the most stable form of cyanomethyl anion and its deuterated forms. For the confirmation of the detection of the cyanomethyl anion and its two deuterated forms, namely, CHDCN- and CD2CN-, we present the rotational spectral information of these species in the Appendix. Our chemical model predicts that the deuterated forms of cyanomethyl radicals (specially the anions) are also reasonably abundant around the dense region of the molecular cloud.

55 pages, 4 figures, accepted for the publication in A&A

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