Full-Dimensional Quantum Reaction Rate Calculations for H + CH₄ → H₂ + CH₃ on a Recent Potential Energy Surface

Abstract

The thermal rate constant of the H + CH(4) → H(2) + CH(3) reaction on the recent potential energy surface (PES) of Corchado et al (CBE) (Corchado, J. C.; Bravo, J. L.; Espinosa-Garcia, J. J. Chem. Phys. 2009, 130, 184314) is computed employing the state-averaged multiconfigurational time-dependent Hartree approach in the temperature range 250-500 K. The CBE PES is global and is based on an analytic functional form that is fast to evaluate. This surface is therefore potentially useful for testing new quantum dynamics methods, and reference rate constants for this purpose are presented here. The thermal rate constants obtained are compared to results previously obtained on an accurate PES particularly designed for thermal rate constant calculations (Wu, T.; Werner, H.; Manthe, U. Science 2004, 306, 2227). The two sets of rate constants are found to agree almost perfectly.

State-to-state reaction probabilities within the quantum transition state framework

“…Accurate full-dimensional quantum dynamics calculations for six atom reactions have up to now only been presented for cumulative reaction probabilities and thermal rate constants [14][15][16][17][18][19][20][21][22][23] or initial state-selected reaction probabilities 24,25 and studied the H + CH 4 → H 2 + CH 3 , [14][15][16][17][18][19][22][23][24][25] [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] and propagated wave packets representing vibrational states of the activated complex which have been a) Electronic mail: rwelsch@uni-bielefeld.de. b) Electronic mail: uwe.manthe@uni-bielefeld.…”

Rate coefficients and kinetic isotope effects of the X + CH4 → CH3 + HX (X = H, D, Mu) reactions from ring polymer molecular dynamics

“…17 This PES was chosen because of its numerical efficiency and the existence of tunneling corrected TST 18 as well as MCTDH calculations, 34 which indicated a good agreement with experiment. RPMD calculations have also been reported for the H + CH 4 reaction on this PES, but only at 300 K. 56 Comparison with the converged Shepard interpolated PES developed by Wu et al 16 indicated that this PES is very accurate for the H + CH 4 rate coefficients.…”

“…[14][15][16][17][18][19][20][21] However, a full-dimensional quantum mechanical treatment of the reaction dynamics is still very difficult. With the exception of the multidimensional time-dependent Hartree [22][23] (MCTDH) calculations, [24][25][26][27][28][29][30][31][32][33][34][35] most quantum dynamical studies of this reaction have been cast in reduced-dimensional models, [36][37][38][39][40][41][42][43][44][45] due to the exponential scaling laws of CPU and memory requirements. Even in the MCTDH work, the J-shifting approximation 46 had to be used in order to make the calculations feasible.…”

“…[57][58] To this end, each quantum particle is represented by a ring polymer made up of a number of beads connected with harmonic potentials. 64 In this work, the RPMD rate coefficients for the title reactions and KIEs were generated using a recent ab initio calibrated empirical PES, 17 on which TST 18 and MCTDH calculations 34 have been reported.…”

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

“…Beside the investigation of gas phase systems (here further calculations ranging from triatomic [76,77] to hexatomic reactions [78][79][80] could be mentioned) also rates for process on surfaces [81,82] and reactions in condensed phase [83,84] studied based on the quantum transition state concept. The dissociative adsorption of N 2 on a stepped Ru-surface was studied by 6D quantum dynamics calculations for a rigid Ru-surface [82] and the effect of surface motion on in the system was considered on TST level [85].…”