Variational transition state theory calculations of thermal rate coefficients for the Q(3P) + HCl reaction

Thomas C. Allison, B. Ramachandran, Jörg Senekowitsch, Donald G. Truhlar, Robert E. Wyatt

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Variational Transition State Theory (VTST) calculations of the thermal rate coefficients of the reaction of O(3P) with HCl are presented. Four potential surfaces for the 3A″ state are studied, three of them due to Ramachandran, Senekowitsch and Wyatt (RSW), based on fits to scaled MR-CISD + Q energies, and the fourth due to Koizumi, Schatz and Gordon (KSG), based on scaled MP2/6-31G(d,p) energies. Using the program POLYRATE, version 7.3, the rate coefficients are calculated using Improved Canonical Variational Theory (ICVT) with the microcanonical Optimized Multidimensional Tunneling (μOMT) approximation over the temperature range 200-1500K. These results are compared to available experimental data, which lie in the range 293-1486K. It is found that the RSW surfaces yield thermal rate coefficients that are in reasonable agreement with experimental data over this range, and in very good agreement for T > 500K, while those computed on the KSG surface are somewhat higher. These comparisons indicate that one of the RSW surfaces may establish an upper limit for the correct reaction barrier for this reaction, while the KSG surface could provide a lower limit.

Original languageEnglish (US)
Pages (from-to)307-314
Number of pages8
JournalJournal of Molecular Structure: THEOCHEM
Issue number2-3
StatePublished - Nov 28 1998

Bibliographical note

Funding Information:
This research is supported by a grant to B.R. from the Louisiana Education Quality Support Fund, under contract no. LEQSF (1994-97)-RD-A-18. R.E.W. acknowledges support from the National Science Foundation and the Welch Foundation, and D.G.T. acknowledges support from the US Department of Energy, Office of Basic Energy Sciences. We are grateful to Drs Javier Aoiz and Juan E. Verdasco for sending us a subroutine to evaluate the KSG potential surface and its derivatives, and to Dr B. Poirier for sending us the quantal rate coefficients from Refs [45, 46] .


  • Potential surfaces
  • Rate coefficients
  • Reaction barriers
  • Transition state theory


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