  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.
