title: Statistical modelling of NH+/ND+ + H2/HD/D2 branching ratios.
abstract: In this work we study hydrogen isotope fractionation along the proposed gas-phase ammonia formation pathway at temperatures relevant to interstellar modelling. Specifically we study the isotopically substituted variants of the NH(+) + H(2) reaction, for which the primary product is NH(2)(+) + H. Adiabatic capture theory calculations have been performed for the association reaction. A new potential-energy surface has been determined for the NH(2)(+) product. An extensive set of rovibrational energy levels has been calculated for the NH(2)(+) isotopologues described by this potential-energy surface. These rovibrational energy levels have been used to determine energy- and angular-momentum-resolved numbers of accessible product states from the NH(3)(+) isotopologue intermediates, which in turn have been averaged to give statistical branching fractions for all isotopically-substituted NH(+) + H(2) reactions. It is determined that in all cases where both hydrogen and deuterium are present, the NHD(+) product is preferred.
authors.affiliation: Physical Chemistry, Department of Chemistry, Göteborg University, Göteborg, Sweden. tjf@rsc.anu.edu.au
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Frankcombe
authors.forename: Gunnar
authors.initials: G
authors.lastname: Nyman
mesh_terms: D000641:Ammonia / Q000737:chemistry*; D003903:Deuterium / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D008956:Models, Chemical; D015233:Models, Statistical; D011789:Quantum Theory; D012399:Rotation; D013696:Temperature; D014732:Vibration
chemical_list: D005740:Gases; D000641:Ammonia; D006859:Hydrogen; D003903:Deuterium