A search for SH(+) and CH(+) in diffuse and translucent clouds

Abstract

Results are reported from a search for SH(+) absorption at about 336 nm from diffuse interstellar clouds and high-latitude molecular clouds in the direction of nine early-type stars. Two of the lines of sight in the direction of translucent high-latitude molecular clouds were also searched for CH(+) absorption at 4232 nm. Both CH(+) and SH(+) are believed to be formed by endothermic reactions which require the passage of a shock through the diffuse cloud. SH(+), in particular, is thought to form as a consequence of an MHD shock. SH(+) was not detected from any of the lines of sight, nor was CH(+) detected from either of the high-latitude clouds. The N(SH+) upper limits obtained are marginally inconsistent with the presence of MHD shocks with velocities greater than 14 km/s, and the nondetections of CH(+) for the high-latitude clouds are inconsistent with current shock-chemistry models. 28 refs.