The Astrochemistry of H3+

Professor E Herbst
Department of Physics and Astronomy, Ohio State University, USA

The molecular ion H3+ is of fundamental importance for the gas-phase chemistry of dense interstellar clouds. The species is produced through ionization of molecular hydrogen by cosmic rays and X-rays. Once synthesized, it acts as a precursor to many other interstellar molecules. For example, the reaction of H3+ with atomic oxygen leads to the formation of interstellar water and OH radical, while the reaction with atomic carbon leads to the formation of simple hydrocarbons such as methane. The exchange reaction between H3+ and interstellar HD is a major contributor to the strong deuterium fractionation observed in dense clouds. Interestingly, the reaction between H3+ and atomic N does not occur; the absence of this reaction removes a rapid pathway for the production of ammonia. Although the chemistry of H3+ in dense interstellar clouds is well understood, its chemistry in diffuse interstellar clouds is currently much more mysterious.