Vibrational excitation in the transition state: The CH4+H→CH3+H2 reaction rate constant in an extended temperature interval

Abstract

Accurate quantum mechanical results for the thermal rate constant of the prototypical six atom reaction, CH4+H→CH3+H2, are reported in this article. Previous k(T) results for temperature values below 500 K are extended up to 1000 K. This is achieved employing a combined iterative diagonalization and statistical sampling approach for the evaluation of the flux correlation function. The accurate reaction rate data obtained for the extended temperature range is used to test several approximations related to the transition state theory. The study especially focuses on the contribution of vibrationally excited states of the activated complex to the thermal rate constant.

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.…”

Communications: A rigorous transition state based approach to state-specific reaction dynamics: Full-dimensional calculations for H+CH4→H2+CH3

“…This reaction has emerged as the prototypical benchmark example of a X +CH 4 reaction studied in theoretical research. [4][5][6]8,9,[13][14][15][17][18][19][20][21][22][23][24][25] Most of this research has been based on the Jordan-Gilbert potential energy surface ͑JG PES͒. 26 To allow comparison with previous theoretical work, the JG PES is used also in the present work despite the fact that meanwhile a more accurate global 25 PES has become available.…”

“…Rigorous full-dimensional quantum dynamics calculations for X +CH 4 reactions have been restricted to the calculation of thermal rate constants and cumulative reaction probabilities for J =0. [4][5][6][7][8][9][10][11][12] Quantum mechanical studies of state-resolved observables have been restricted to reduced-dimensional calculations. The most elaborate studies could include six to seven degrees of freedom explicitly.…”

The reaction rate for dissociative adsorption of N2 on stepped Ru(0001): Six-dimensional quantum calculations

“…This was also found in previous calculations for gas-phase systems. 22,23 The rotational and vibrational partition functions of N 2 have been computed within the rigid rotor and the harmonic oscillator approximations, respectively. Relevant PES data obtained from DFT calculations are given in Table IV.…”

“…The combination of the flux correlation approach with the multiconfiguration time-dependent Hartree ͑MCTDH͒ scheme for efficient multidimensional wave-packet propagation made it possible to study the quantum dynamics of 12-dimensional systems. [20][21][22][23][24][25] The previous studies show that quantum effects are significant in reactions where hydrogen atoms are transferred. At room temperature the tunneling effect often increases the reaction rate by one order of magnitude.…”