Rate constants for H + CH₄, CH₃ + H₂, and CH₄ dissociation at high temperature

Abstract

The Laser Photolysis-Shock Tube technique coupled with H-atom atomic resonance absorption spectrometry has been used to study the reaction, H + CH 4 → CH 3 + H 2 , over the temperature range, 928-1697 K. Shock-tube studies on the reverse of this reaction, CH 3 + H 2 → H + CH 4 , using CH 3 I dissociation in the presence of H 2 yielded H-atom formation rates and rate constants for the reverse process over the temperature range, 1269-1806 K. These results were transformed (using well-established equilibrium constants) to the forward direction. The combined results for H + CH 4 can be represented by an experimental three parameter expression, k = 6.78 × 10 −21 T 3.156 exp(−4406 K/T ) cm 3 molecule −1 s −1 (348-1950 K) that was evaluated from the present work and seven previous studies. Using this evaluation, disagreements between previously reported values for the dissociation of CH 4 could be reconciled. The thermal decomposition of CH 4 was then studied in Kr bath gas. The dissociation results agreed with the earlier studies and were theoretically modeled with the Troe formalism. The energy transfer parameter necessary to explain both the present results and those of Kiefer and Kumaran (J Phys Chem 1993, 97, 414) is, − E all /cm −1 = 0.3323 T 0.7 . The low temperature data on the reverse reaction, H + CH 3 (in He) from Brouard et al. (J Phys Chem 1989, 93, 4047) were also modeled with the Troe formalism. Lastly, the rate constant for H + CH 4 was theoretically calculated using conventional transition state theory with Eckart tunneling corrections. The potential energy surface used was from Kraka et al. (J Chem Phys 1993, 99, 5306) and the derived T-dependence with this method agreed almost perfectly with the experimental evaluation.

Trajectory Dynamics Study of the Ar + CH4 Dissociation Reaction at High Temperatures: the Importance of Zero-Point-Energy Effects

“…From a first glance of Figure 6, we observe that our results are in reasonable agreement with the estimations of Miller et al 11 and, at least, in qualitative agreement with those of Sutherland et al 12 for Kr + CH 4 Another important feature from Figure 6 is that both 〈∆E d 〉 and 〈∆E 2 〉 1/2 vary more rapidly with temperature than 〈∆E〉. Thus, as has been advocated by Miller et al, 11 assuming 〈∆E〉 (despite 〈∆E d 〉) as independent of temperature may be a reasonable first approximation for modeling unimolecular reactions whenever better information is not available.…”

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

“…In this work, we apply a full-dimensional approximate quantum mechanical method, namely ring-polymer molecular dynamics (RPMD), to calculate the rate The overall agreement with experimental rate coefficient is good for the H + CH 4 reaction, particularly with the latest measurement by Sutherland et al 6 Sutherland et al, 6 and the recommended values from Baulch et al …”

“…To our best knowledge, there has not been any more recent work on this reaction. Given the much smaller rate coefficients recommended by Baulch et al 8 and by Sutherland et al 6 for the H + CH 4 reaction, it is likely that the rate coefficient in the study of Kurylo et al 3 were also overestimated for the D + CH 4 reaction. 29 In other words, we believe that the theoretical rate coefficients are probably more accurate than their experimental counterparts.…”

“…1 The rate coefficient of the reaction is well known over a large temperature range. [2][3][4][5][6][7][8] It has also served as a benchmark for understanding bimolecular reaction dynamics involving polyatomic molecules. [9][10][11] Due to the involvement of light hydrogenic atoms, the reaction is intrinsically quantum mechanical.…”

H + CD4 Abstraction Reaction Dynamics: Excitation Function and Angular Distributions

“…As a result it has long served as a benchmark for theoretical studies of atom plus polyatomic molecule reactions. 11,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Much of this work has been concerned with determination of stationary point properties and the rate constants, although occasionally there has been work on the state-resolved dynamics. Many potential energy surfaces (PES) have been developed.…”