The astrochemistry of H 3 +

The reactions of the molecular ion H3+ are pivotal to the chemistry of dense interstellar clouds. Produced by the cosmic-ray ionization of molecular hydrogen, H3 + reacts with a variety of atoms and molecules to produce species that are precursors to many of the detected molecules in dense clouds. For example, the reaction of H3+ with atomic O leads, eventually, to the production of water, while the reaction with HD leads to the production of a wide variety of deuterated isotopomers. In this article, the chemistry of H3+ and the products derived from it are discussed in the larger context of interstellar chemistry.