A reduced dimensionality, six-degree-of-freedom, quantum calculation of the H+CH4→H2+CH3 reaction

Abstract

A reduced dimensionality, time-dependent wave-packet calculation is reported for the H+CH4→H2+CH3 reaction in six degrees of freedom and for zero total angular momentum, employing the Jordan–Gilbert potential energy surface. Reaction probabilities for seven initial vibrational states of nonrotating “CH4,” and for the three lowest energy vibrational states and numerous initial rotational states are presented. Excitation of the C–H stretch, and the bending of H–CH3, enhances the reaction probability more than excitation of the umbrella mode. The six-degree-of-freedom cumulative reaction probability (CRP) for zero total angular momentum is obtained by direct summation over initial state-resolved reaction probabilities. An approximate full-dimensional CRP for zero total angular momentum is obtained using the energy-shift approximation to account for the contribution of degrees of freedom missing in the reduced dimensionality calculations. Then J–K shifting is applied to this CRP to obtain the thermal rate constant which is compared with previous calculations.

A permutationally invariant full-dimensional ab initio potential energy surface for the abstraction and exchange channels of the H + CH4 system

“…[28][29][30][31][32][33][34][35][36] On the theoretical front, the reaction dynamics has been investigated using both quasi-classical trajectory (QCT) 22,[37][38][39][40][41][42] and quantum dynamical (QD) methods. While many of the QD studies were based on reduced-dimensional models, [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] full-dimensional calculations of the reaction dynamics have been reported by Manthe and coworkers at both the initial state selected [59][60][61][62] and state-to-state levels, 63 using the multiconfiguration time-dependent Hartree (MCTDH) approach.…”

Comparison between different reactions of group IV hydride with H

“…Theoretically, quantum dynamic study of reactions beyond four atoms is extremely difficult due to the computation cost with the increase of system dimension [1] . To solve this problem, a number of methods have been proposed [2][3][4][5][6][7][8][9] . The semirigid vibrating rotor target (SVRT) model [10][11][12][13][14][15] is a reduced dimensionality model that is general for studying polyatomic systems.…”

Accurate calculations of reaction rates: predictive theory based on a rigorous quantum transition state concept

“…Studying a reaction where quantum effects are important, one might consider to avoid rigorous full-dimensional calculations and to employ a reduced-dimensional description to account for the quantum effects present. Several reduced-dimensional models were investigated for benchmark reactions as H + CH 4 → H 2 + CH 3 [78,[103][104][105][106][107][108][109] or H 2 + OH → H + H 2 O [110, 111] and compared to accurate fulldimensional results. Depending on the choice of the coordinates explicitly included and the modeling used to account for the neglected degrees of freedom, results of varying accuracy have been obtained.…”