Formation of CO in the Reaction of O Atoms with CH3: Reaction Over a Barrier but not Through a Saddle Point

Published

June 1, 2002

Author(s)

Vadim D. Knyazev

Abstract

A new type of chemical reaction characterized by a reaction path proceeding over an energy barrier (a ridge of the potential energy surface) but not through a saddle point is described. A method of computation of rate constants for such over-the-ridge reactions is developed on the basis of RRKM and transition state theories. Formulas and computational procedures are presented for the cases of microscopic energy-dependent rates of unimolecular reactions and the thermally averaged rates of unimolecular or bimolecular reactions. This method is applied to compute the branching fraction of the CO-producing channel (channel 1c) of the reaction of O atoms with CH₃ radicals. A quantum chemical computational study of the potential energy surface (PES) of the decomposition of CH₃O was performed using UHF, UMP2, QCISD, and B3LYP methods as well as single-point G2 and CBS-Q energy calculations. The results demonstrate that the products of the reaction channel 1c are formed in a process characterized by trajectories in coordinate space that proceed over a potential energy ridge but not through a saddle point. The method developed in this work was used to calculate the microscopic energy-dependent rate constants of the decomposition of CH₃O and the branching fraction of the reaction channel 1c. The calculated values of the channel 1c fraction, 2.5 % to 5 % (depending on the potential energy surface used), are in moderate, order-of-magnitude agreement with the reported experimental results which range from 18 4 % to 40 10 %.

Citation

Journal of Physical Chemistry A

Volume

36-Issue# 37

Pub Type

Journals

Keywords

CH₃O, CO, potential energy surface, ridge, RRKM, unimolecular reaction

Citation

Knyazev, V. (2002), Formation of CO in the Reaction of O Atoms with CH3: Reaction Over a Barrier but not Through a Saddle Point, Journal of Physical Chemistry A (Accessed April 18, 2024)