H_{2}S 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 H_{2}S in two prototypical dark clouds, TMC1 and Barnard 1, to shed light on the physical and chemical processes involved in H_{2}S creation and destruction. Our observations are consistent with a PDR model in which H_{2}S 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 H_2S abundance.