Six-dimensional and seven-dimensional quantum dynamics study of the OH + CH4 → H2O + CH3 reaction

Abstract

The reaction dynamics of hydroxyl radical with methane has been investigated using time-dependent wave packet approach within reduced six- and seven-dimensional models. Initial state-selected total reaction probabilities and integral cross sections for the hydrogen abstraction reaction have been computed on the empirical potential energy surface developed by Espinosa-García et al. [J. Chem. Phys. 112, 5731 (2000)]. Excitations of the CH stretching mode and/or the CH3 umbrella mode enhance the reaction. They are, however, both less efficient than translational energy in promoting the reaction, at least at low collision energies. Also, we studied the accuracy of two approximations: centrifugal sudden (CS) and J-shifting (JS), in the calculations of the integral cross sections by a comparison to coupled-channel (CC) calculations. The integral cross sections obtained indicated that the CS approximation works well over the whole energy range studied, and the JS approximation gives accurate cross sections at low collision energies, while noticeably overestimates them at relatively high collision energies. In addition, the OH radical acts as a good spectator as it has a negligible effect on the reaction.

Product Translational and Vibrational Distributions for the OH/OD + CH4/CD4 Reactions from Quasiclassical Trajectory Calculations. Comparison with Experiment.

“…(b) 1GB harmonic exact (1GB-harm-exac): While the E(n) energy is calculated in the same way (eq 7), the E(n′) energy is determined exactly in the Cartesian space as (8) where T is the vibrational kinetic energy of product p and ΔV is the difference between the potential energies of the equilibrium geometry and the geometry of the products at the final step of the reactive trajectory.…”

Communication: An accurate full 15 dimensional permutationally invariant potential energy surface for the OH + CH4 → H2O + CH3 reaction

“…The first full-dimensional PES for the title reaction was constructed by EspinosaGarcia and co-workers using a molecular mechanics functional form based on both theoretical and experimental information. 25 Several kinetics and dynamics calculations have since been performed on this so-called PES-2000, [25][26][27][28][29][30] and the agreement with available experimental data has generally been good. A refined PES, PES-2014, was later constructed by fitting exclusively to ab initio data, using essentially the same approach.…”

Recent advances in quantum scattering calculations on polyatomic bimolecular reactions

“…Crossed molecular beam experiments were carried out to study the state-to-state dynamics for the OH+CD4 reaction by Liu and coworkers [270][271][272] . The early quantum dynamics calculations were restricted to two-three degrees of freedom 273,274 , and then more degrees of freedom up to seven [275][276][277] were included to investigate the reaction dynamics, partly due to the emergence of accurate global PESs. The first global PES was constructed by Espinosa-García and Corchado based on an analytical function (PES-2000) 278 , which was further refined by them (PES-2014).…”

“…Recently, six-dimensional (6D) and seven-dimensional (7D) ISSWP calculations were performed on the PES-2000 276,277 . The 6D and 7D Hamiltonians were mainly based on the Palma-Clary model, which restricted the nonreactive CH3 group in the C3v symmetry 214 .…”