  The nature of the main sulphur reservoir in star forming regions is a long
standing mystery. The observed abundance of sulphur-bearing species in dense
clouds is only about 0.1 per cent of the same quantity in diffuse clouds.
Therefore, the main sulphur species in star forming regions of the interstellar
medium are still unknown. IRAS 16293-2422 is one of the regions where
production of S-bearing species is favourable due to its conditions which
allows the evaporation of ice mantles. We carried out observations in the 3 mm
band towards the solar type protostar IRAS 16293-2422 with the IRAM 30m
telescope. We observed a single frequency setup with the EMIR heterodyne 3 mm
receiver with an Lower Inner (LI) tuning frequency of 89.98 GHz. Several lines
of the complex sulphur species CH3SH were detected. Observed abundances are
compared with simulations using the NAUTILUS gas-grain chemical model.
Modelling results suggest that CH3SH has the constant abundance of 4e-9
(compared to H2) for radii lower than 200 AU and is mostly formed on the
surfaces. Detection of CH3SH indicates that there may be several new families
of S-bearing molecules (which could form starting from CH3SH) which have not
been detected or looked for yet.
