Nuclear spin dependence of the reaction of H3+with H2. I. Kinetics and modeling

Kyle N. Crabtree, Brian A. Tom, Benjamin J. McCall

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The chemical reaction H3+ H2 → H 2 H3+ is the simplest bimolecular reaction involving a polyatomic, yet is complex enough that exact quantum mechanical calculations to adequately model its dynamics are still unfeasible. In particular, the branching fractions for the identity, proton hop, and hydrogen exchange reaction pathways are unknown, and to date, experimental measurements of this process have been limited. In this work, the nuclear-spin-dependent steady-state kinetics of the H3+ H2 reaction is examined in detail, and employed to generate models of the ortho:para ratio of H3+ formed in plasmas of varying ortho:para H2 ratios. One model is based entirely on nuclear spin statistics, and is appropriate for temperatures high enough to populate a large number of H 3+ rotational states. Efforts are made to include the influence of three-body collisions in this model by deriving nuclear spin product branching fractions for the H5+ H2 reaction. Another model, based on rate coefficients calculated using a microcanonical statistical approach, is appropriate for lower-temperature plasmas in which energetic considerations begin to compete with the nuclear spin branching fractions. These models serve as a theoretical framework for interpreting the results of laboratory studies on the reaction of H3+ with H2.

Original languageEnglish (US)
Article number194310
JournalJournal of Chemical Physics
Issue number19
StatePublished - May 21 2011

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry


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