Observations of H₂S toward OMC-1

Interstellar hydrogen sulfide (H₂S) and its isotopic variant (H₂³⁴S) have been observed toward several positions in OMC-1 via their 1₁₀-1₀₁ transitions near 168 GHz using the FCRAO 14 m telescope. We derive total column densities toward Orion(KL) for the extended ridge, for the plateau, and for the hot core, in addition to values for other positions in OMC-1. The fractional abundance of H₂S (∼ 10^-9) in the quiescent regions of OMC-1 seems to be difficult to explain by currently known ion-molecule reactions. The fractional abundance of H₂S relative to H₂ is enhanced by a factor of 1000 in the hot core and the plateau relative to the quiescent clouds. This enhancement may be a result of grain surface chemistry and/or of high-temperature gas-phase chemistry. From the nondetection of HDS in its 2₁₁-2₁₂ transition, we estimate the abundance ratio [HDS]/[H₂S] ≤ 0.02 in the hot core.