2002ApJ...578L..87S

The recent detection of the metastable HOC⁺ isomer toward a wide range of interstellar environments has demonstrated abundances that cannot be explained within current chemical models. The abundance of HOC⁺ in these models relies heavily on the rate of the isomerization of HOC⁺ by H₂to the lowest energy isomer, HCO⁺. A variable temperature 22-pole ion-trap apparatus is employed to study the isomerization of HOC⁺ by H₂at 25 K. The observed rate coefficient for isomerization is (3.8±0.5)x10^–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.