Deuterium Enrichment of the Interstellar Medium
  Despite low elemental abundance of atomic deuterium in interstellar medium
(ISM), observational evidences suggest that several species in gas-phase and in
ices could be heavily fractionated. We explore various aspects of deuterium
enrichment by constructing a chemical evolution model in gas and grain phases.
Depending on various physical parameters, gas and grains are allowed to
interact with each other through exchange of their chemical species. It is
known that HCO+ and N2H+ are two abundant gas phase ions in ISM and their
deuterium fractionation are generally used to predict degree of ionization in
various regions of a molecular cloud. To have a more realistic estimation, we
consider a density profile of a collapsing cloud. We present radial
distributions of important interstellar molecules along with their deuterated
isotopomers. We carry out quantum chemical simulation to study effects of
isotopic substitution on spectral properties of these important interstellar
species. We calculate vibrational (harmonic) frequency of the most important
deuterated species (neutral & ions). Rotational and distortional constants of
these molecules are also computed to predict rotational transitions of these
species. We compare vibrational (harmonic) and rotational transitions as
computed by us with existing observational, experimental and theoretical
results. We hope that our results would assist observers in their quest of
several hitherto unobserved deuterated species.
