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A product branching ratio controlled by vibrational adiabaticity and variational effects: kinetics of the H + trans-N2H2 reactions.

Authors
  • Zheng, Jingjing1
  • Rocha, Roberta J
  • Pelegrini, Marina
  • Ferrão, Luiz F A
  • Carvalho, Edson F V
  • Roberto-Neto, Orlando
  • Machado, Francisco B C
  • Truhlar, Donald G
  • 1 Department of Chemistry and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455-0431, USA.
Type
Published Article
Journal
The Journal of Chemical Physics
Publisher
American Institute of Physics
Publication Date
May 14, 2012
Volume
136
Issue
18
Pages
184310–184310
Identifiers
DOI: 10.1063/1.4707734
PMID: 22583290
Source
Medline
License
Unknown

Abstract

The abstraction and addition reactions of H with trans-N(2)H(2) are studied by high-level ab initio methods and density functional theory. Rate constants were calculated for these two reactions by multistructural variational transition state theory with multidimensional tunneling and including torsional anharmonicity by the multistructural torsion method. Rate constants of the abstraction reaction show large variational effects, that is, the variational transition state yields a smaller rate constant than the conventional transition state; this results from the fact that the variational transition state has a higher zero-point vibrational energy than the conventional transition state. The addition reaction has a classical barrier height that is about 1 kcal∕mol lower than that of the abstraction reaction, but the addition rates are lower than the abstraction rates due to vibrational adiabaticity. The calculated branching ratio of abstraction to addition is 3.5 at 200 K and decreases to 1.2 at 1000 K and 1.06 at 1500 K.

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