  Recent laboratory measurements for the S^+2 + H2 reaction find a total rate
coefficient significantly larger than previously used in theoretical models of
X-ray dominated regions (XDRs). While the branching ratio of the products is
unknown, one energetically possible route leads to the SH+ molecule, a known
XDR diagnostic. In this work, we study the effects of S^+2 on the formation of
SH+ and the destruction of S^+2 in XDRs. We find the predicted SH+ column
density 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 dominant
pathway to SH+, which then initiates the formation of other sulfur-bearing
molecules. We also find that the high rate of S^+2 + H2 efficiently destroys
S^+2 once H2 forms, while the S^+2 abundance remains high in the atomic
hydrogen region. We discuss the possible consequences of S^+2 in the atomic
hydrogen region on mid-infrared diagnostics. The enhanced SH+ abundance has
important implications in the study of XDRs, while our conclusions for S^+2
could potentially impact the interpretation of Spitzer and SOFIA observations.

Astrophysics