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