Abundances of hydrogen sulfide in star-forming regions

Interstellar hydrogen sulfide (H₂S) and its isotopic variant H₂³⁴S have been observed toward several star-forming regions via their 1₁₀-1₀₁ transitions at 2 mm, using the FCRAO telescope. In sources where both isotopic species H₂S and H₂³⁴S were observed, column densities of ∼10¹⁶ cm^-2 were measured. Column density lower limits of ∼10¹⁴ cm^-2 for H₂S were found for other sources, where only the main isotopic line was observed. The fractional abundances of H₂S relative to molecular hydrogen appear to be enhanced by at least an order of magnitude relative to quiescent cloud values (- 10^-9) for many of the observed sources. Such enhancement toward star-forming clouds suggests that some process involving elevated temperature aids in producing this species; this could be gas-phase reactions, grain-related processes, or both.