AAS 201st Meeting, January, 2003
Session 47. The Interstellar Medium I
Poster, Tuesday, January 7, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[47.10] HOC+ + H2 Isomerization Rate at 25K: Implications on the Observed [HCO+]/[HOC+] Ratios in the Interstellar Medium

M. A. Smith (University of Arizona), S. Schlemmer, J. v. Richthofen, D. Gerlich (Chemnitz University)

Recent detection of the metastable HOC+ isomer toward a wide range of interstellar environments has demonstrated abundances which cannot be explained within current chemical models. The abundance of HOC+ in these models relies heavily upon the rate of isomerization of HOC+ by H2 to the lowest energy isomer, HCO+. A variable temperature 22-pole ion trap apparatus is employed to study the isomerization of HOC+ by H2 at 25 K. The observed rate coefficient for isomerization is (3.8 ± 0.5) x 10-10 cm3 s-1. This indicates that there is probably no temperature dependence in this reaction below 300 K, suggesting the absence of any significant energetic barrier on the lowest adiabatic H3CO+ potential surface. This result argues that in regions where abundant HOC+ is observed, the production of this isomer must be strongly favored or that there is a concomitant rapid physicochemical loss for the isomer HCO+. Some results for forming DCO+ are briefly mentioned.

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