# On the reservoir of sulphur in dark clouds : chemistry and elemental abundance reconciled

## TL;DR

This study enhances sulphur chemical modeling in dark clouds by updating reaction networks, revealing sulphur reservoirs vary with cloud age, and successfully reproduces observed sulphur species using cosmic sulphur abundance.

## Contribution

The paper introduces an improved sulphur chemical network based on experimental and theoretical data, enabling better modeling of sulphur reservoirs in dark clouds.

## Key findings

- Sulphur can be in atomic form or as HS and H2S in icy grains depending on cloud age.
- Updated model reproduces observed sulphur species in TMC-1 (CP) using cosmic sulphur abundance.
- The sulphur reservoir varies with the evolutionary stage of the dark cloud.

## Abstract

Sulphur-bearing species are often used to probe the physical structure of star forming regions of the interstellar medium, but the chemistry of sulphur in these regions is still poorly understood. In dark clouds, sulphur is supposed to be depleted under a form which is still unknown despite numerous observations and chemical modeling studies that have been performed. In order to improve the modeling of sulphur chemistry, we propose an enhancement of the sulphur chemical network using experimental and theoretical literature. We test the effect of the updated network on the outputs of a three phases gas-grain chemical model for dark cloud conditions using different elemental sulphur abundances. More particularly, we focus our study on the main sulphur reservoirs as well as on the agreement between model predictions and the abundances observed in the dark cloud TMC-1 (CP). Our results show that depending on the age of the observed cloud, the reservoir of sulphur could either be atomic sulphur in the gas-phase or HS and H2S in icy grain bulks. We also report the first chemical model able to reproduce the abundances of observed S-bearing species in TMC-1 (CP) using as elemental abundance of sulphur its cosmic value.