Deuterium Enrichment of the Interstellar Medium

TL;DR

This paper models deuterium enrichment in the interstellar medium by combining chemical evolution, quantum chemical simulations, and spectral predictions to aid observational detection of deuterated molecules.

Contribution

It introduces a comprehensive model integrating gas-grain chemistry, density profiles, and spectral calculations for deuterated interstellar molecules, enhancing understanding and detection.

Findings

Radial distributions of interstellar molecules and their deuterated isotopomers are presented.

Spectral properties of deuterated species are predicted and compared with existing data.

The model aids in identifying unobserved deuterated molecules in the interstellar medium.

Abstract

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.