Sulfuretted Molecules in Hot Cores

摘要

The chemistry of sulfur-bearing molecules that result from grain-mantle evaporation into warm gas is described. Evaporation of ices, in which all the available sulfur is contained in H2S, drives a hot-phase chemistry that produces SO, SO2, CS, OCS, and H2CS. It is predicted that S2 can attain significant abundances in hot cores. Large variations in abundances occur as a core evolves, and eventually almost all the original H2S is converted to SO and SO2. The SO/H2S and SO/SO2 abundance ratios could be useful as a crude molecular clock to measure the time since mantles were disrupted. Model calculations can reasonably explain the observed distribution of S-bearing molecules in the Orion Hot Core, the Orion Compact Ridge, and in Sgr B2N. In these sources, the theory requires that OCS be formed on grain surfaces. Hot core chemistry alone cannot explain the sulfur chemistry in the Sgr B2M source.