A quasiclassical trajectory study of the Cl + HCN → HCl + CN reaction dynamics. Microscopic reaction mechanism of the H(Cl) + HCN → H2(HCl) + CN reactions

Diego Troya, Miguel González, Guosheng Wu, George C Schatz

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The Cl + HCN → HCl + CN reaction dynamics has been studied using the quasiclassical trajectory method. The potential energy surface is taken from an accurate global surface for the HHCN system. Cl + HCN and H + HCN have very similar energetics, so the present calculation provides a test of whether the Cl + HCN dynamics is captured by a model in which the only difference is provided by the mass of the attacking atom. We find generally good agreement with experimental studies of the Cl + HCN reaction, including CN product rovibrational distributions and the relative rate coefficients for HCN initially in highly excited vibrational states. The results correctly describe the differences between Cl and H attack, so apparently the differences in the reactivity of these two reactions are a kinematic effect. A detailed analysis of the microscopic reaction mechanism of the H + HCN → H2 + CN and Cl + HCN → HCl + CN reactions is also provided. This shows that the H and Cl reactions are both dominated by direct dynamics; however, the direct reaction with Cl frequently involves secondary collisions in which the Cl interacts with the CN fragment of HCN before abstracting the H atom, while the H atom reaction rarely does this. This allows the CN stretch mode to interact more strongly with reaction coordinate motions in Cl + HCN than in H + HCN, leading to greater CN vibrational excitation for initial HCN states that have no C-N stretch excitation, in agreement with observations.

Original languageEnglish
Pages (from-to)2285-2297
Number of pages13
JournalJournal of Physical Chemistry A
Issue number11
Publication statusPublished - Mar 22 2001


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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