Quantum Mechanical Capture/Phase Space Theory Calculation of the Rate Constants for the Complex-Forming CH + H2 Reaction

摘要

Six-dimensional wave packet calculations on an accurate potential energy surface are used to obtain the quantum mechanical capture(QM C)probabilities for CH + H2 corresponding to a variety of total angular momenta and internal reactant states.Rate constant calculations are made feasible by employing a Monte Carlo based sampling procedure.The QM C probabilities alone are also used to estimate the high pressure.CH + H2 rate constants corresponding to stabilization or CH3 formation.The rate constants for CH + H2->CH2 + H reaction in the low pressure limit are obtained by combining the QM C probabilities with a phase space theory(PST)approximation for product formation from the complex.Our results are compared with the experimental results of Brownsword et al.(J.Chem.Phys.1997,106,7662),as well as with purely classical PST calculations.The QM C probabilities are shown to be highly dependent on the initial rotational states of the reactants corresponding to orientational restrictions on complex formation.Consistent with this,our QM C high pressure rate constants for CH3 formation are lower than the purely classical PST rate constants.These QM C rate constants also are in reasonable accord with experiment.A similar but somewhat more subtle picture emerges regarding the QM C/PST rate constants for CH2 + H formation.