TY - JOUR

T1 - Sensitivity of the H + CH3 → CH4 recombination rate constant to the shape of the CH stretching potential

AU - Duchovic, Ronald J.

AU - Hase, William L.

N1 - Funding Information:
This researchw as supportedb y the National Science Foundation. Special thanks to Dr. K.N. Swamy for his assistancei n completing the trajectory calculations.

PY - 1984/10/12

Y1 - 1984/10/12

N2 - Using a potential-energy surface obtained in part from ab initio calculations, the H + CH3 → CH4 bimolecular rate constant at T = 300 K is determined from a Monte Carlo classical trajectory study. Representing the CH stretching potential with a standard Morse function instead ofthe ab initio curve increases the calculated rate constant by an order of magnitude. The experimental recombination rate constant is intermediate of the rate constants calculated with the Morse and ab initio stretching potentials. Two properties of the H + CH3 α CH4 potential-energy surface which significantly affect the recombination rate constant are the shape of the CH stretching potential and the attenuation of the H3CH bending frequencies. Ab initio calculations with a hierarchy of basis sets and treatment of electron correlation indicate the latter is properly described [13]. The exact shape of the CH stretching potential is not delineated by the ab initio calculations, since the ab initio calculations are not converged for bond lengths of 2.0-3.0 Å [12]. However, the form of this stretching potential deduced from the highest-level ab initio calculations, and fit analytically by eq. (2), is significantly different from a Morse function. The experimental recombination rate constant is intermediate of the rate constants calculated with the Morse and ab initio CH stretching potentials. This indicates that the actual CH potential energy curve lies between the Morse and ab initio curves. This is consistent with the finding that potential energy curves for diatomics are not well described by a Morse function [12].

AB - Using a potential-energy surface obtained in part from ab initio calculations, the H + CH3 → CH4 bimolecular rate constant at T = 300 K is determined from a Monte Carlo classical trajectory study. Representing the CH stretching potential with a standard Morse function instead ofthe ab initio curve increases the calculated rate constant by an order of magnitude. The experimental recombination rate constant is intermediate of the rate constants calculated with the Morse and ab initio stretching potentials. Two properties of the H + CH3 α CH4 potential-energy surface which significantly affect the recombination rate constant are the shape of the CH stretching potential and the attenuation of the H3CH bending frequencies. Ab initio calculations with a hierarchy of basis sets and treatment of electron correlation indicate the latter is properly described [13]. The exact shape of the CH stretching potential is not delineated by the ab initio calculations, since the ab initio calculations are not converged for bond lengths of 2.0-3.0 Å [12]. However, the form of this stretching potential deduced from the highest-level ab initio calculations, and fit analytically by eq. (2), is significantly different from a Morse function. The experimental recombination rate constant is intermediate of the rate constants calculated with the Morse and ab initio CH stretching potentials. This indicates that the actual CH potential energy curve lies between the Morse and ab initio curves. This is consistent with the finding that potential energy curves for diatomics are not well described by a Morse function [12].

UR - http://www.scopus.com/inward/record.url?scp=0038221748&partnerID=8YFLogxK

U2 - 10.1016/0009-2614(84)87073-6

DO - 10.1016/0009-2614(84)87073-6

M3 - Article

AN - SCOPUS:0038221748

VL - 110

SP - 474

EP - 477

JO - Chemical Physics Letters

JF - Chemical Physics Letters

SN - 0009-2614

IS - 5

ER -