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Recent laboratory measurements for the S^+2 + H2 reaction find a total ratecoefficient significantly larger than previously used in theoretical models ofX-ray dominated regions (XDRs). While the branching ratio of the products isunknown, one energetically possible route leads to the SH+ molecule, a knownXDR diagnostic. In this work, we study the effects of S^+2 on the formation ofSH+ and the destruction of S^+2 in XDRs. We find the predicted SH+ columndensity for molecular gas surrounding an Active Galactic Nucleus (AGN)increases by as much as 2 dex. As long as the branching ratio for S^+2 + H2 ->SH+ + H+ exceeds a few percent, doubly ionized chemistry will be the dominantpathway to SH+, which then initiates the formation of other sulfur-bearingmolecules. We also find that the high rate of S^+2 + H2 efficiently destroysS^+2 once H2 forms, while the S^+2 abundance remains high in the atomichydrogen region. We discuss the possible consequences of S^+2 in the atomichydrogen region on mid-infrared diagnostics. The enhanced SH+ abundance hasimportant implications in the study of XDRs, while our conclusions for S^+2could potentially impact the interpretation of Spitzer and SOFIA observations.

The Effects of Doubly Ionized Chemistry on SH+ and S^+2 Abundances in X-ray Dominated Regions