H2S Formation in Dark Clouds

Sulfur is of fundamental importance in a wide variety of phenomena such as life on Earth. This element is one of the most abundant elements in space S/H ∼ 1.3×10−5, but sulfuratted molecules are not as abundant as expected, thus a better understanding of sulfur chemistry is needed. We study and model the abundance of H2S in two prototypical dark clouds, TMC1 and Barnard 1, to shed light on the physical and chemical processes involved in H2S creation and destruction. Our observations are consistent with a PDR model in which H2S is formed in grain mantles and released to gas phase via photodesorption. We cannot discard the contribution of other desorption processes, such as chemical desorption and/or grain-grain collisions, to enhance the H2S abundance.