New extended deuterium fractionation model: assessment at dense ISM conditions and sensitivity analysis

TL;DR

This paper introduces an extended deuterium fractionation model with a comprehensive chemical network, tests it against diverse interstellar conditions, and analyzes the sensitivity of D/H ratios to reaction rate uncertainties.

Contribution

It provides a publicly available, updated chemical network for deuterium chemistry and assesses the impact of reaction rate uncertainties on model predictions.

Findings

Many multiply-deuterated species retain high D/H ratios up to 100 K.

Uncertainties in reaction rates are lower in dark clouds than in warm IRDCs.

The model predicts observable deuterated molecules in star-forming regions.

Abstract

Observations of deuterated species are useful in probing the temperature, ionization level, evolutionary stage, chemistry, and thermal history of astrophysical environments. The analysis of data from ALMA and other new telescopes requires an elaborate model of deuterium fractionation. This paper presents a publicly available chemical network with multi-deuterated species and an extended, up-to-date set of gas-phase and surface reactions. To test this network, we simulate deuterium fractionation in diverse interstellar sources. Two cases of initial abundances are considered: i) atomic except for H2 and HD, and ii) molecular from a prestellar core. We reproduce the observed D/H ratios of many deuterated molecules, and sort the species according to their sensitivity to temperature gradients and initial abundances. We find that many multiply-deuterated species produced at 10 K retain enhanced D/H ratios at temperatures $\la 100$ K. We study how recent updates to reaction rates affect calculated D/H ratios, and perform a detailed sensitivity analysis of the uncertainties of the gas-phase reaction rates in the network. We find that uncertainties are generally lower in dark cloud environments than in warm IRDCs and that uncertainties increase with the size of the molecule and number of D-atoms. A set of the most problematic reactions is presented. We list potentially observable deuterated species predicted to be abundant in low- and high-mass star-formation regions.