Monte Carlo transitionhyphen;state study of angular momentum effects on the unimolecular dissociation of CH4on the Duchovicndash;Hasendash;Schlegelab initiosurface

摘要

A previously formulated Monte Carlo transitionhyphen;state theory approach to unimolecular reactions has been extended to the calculation of microcanonical rate coefficients for specific angular momentum states. The method is applied to a study of twohyphen;center dissociation of CH4on the Duchovicndash;Hasendash;Schlegel (DHS)ab initiopotentialhyphen;energy surface. The rotationally averaged microcanonical rate coefficients on the DHS surface are found to be consistently less than those previously calculated on a semiempirical surface due principally to the larger Cndash;H bond dissciation energy on the DHS surface. The rate coefficients are found to be relatively insensitive to the other topographical features of the potentialhyphen;energy surface. Angular momentum is found to reducek(E;J) by an amount in excess of the centrifugal effect. The magnitude of the angular momentum effect is found to decrease as the ratio of the rotational energy to the energy in excess of threshold decreases. Overall, the MCTST procedure is found to be computationally efficient for such calculations.