Dynamics of the O(³P) + CH₄ hydrogen abstraction reaction at hyperthermal collision energies

Abstract

Motivated by recent experiments on the title reaction at the high collision energy of 64 kcal mol(-1) reported by Minton et al., a detailed dynamics study was carried out using quasi-classical trajectory (QCT) calculations based on an analytical potential energy surface recently developed by our group, PES-2014. Our results reproduce the experimental evidence: most of the available energy appears as translational energy (80 ± 10%) and scattering distribution is forward, suggesting a stripping mechanism associated with high impact parameters. Of special interest is the triple (angle-velocity) differential cross section (a combination of translational and scattering distributions), which shows the same structure associated with the products. Agreement with experiment lends confidence to the new PES-2014 surface; this is encouraging, furthermore, because its fitting was made with thermal behaviour in mind, and higher energy areas were neither sampled nor weighted sufficiently.

Quasiclassical trajectory study of the effect of antisymmetric stretch mode excitation on the O(3P) + CH4(ν3 = 1) → OH + CH3 reaction on an analytical potential energy surface. Comparison with experiment

“…With regard to the vibrational ground-state reaction, O( 3 P) + CH 4 (ν = 0), the experimental studies [1][2][3][4][5] have shown that this reaction leads to cold rotational and non-inverted vibrational distributions of the OH product, low vibrational excitation of the CH 3 co-product, and a backward scattering angular distribution. The theoretical studies [6][7][8][9][10][11][12][13][14] are consistent with the experimental finding, associated with a rebound mechanism with a narrow cone of acceptance and a collinear CH 3 -H -O transition state. Recently, we reported a series of theoretical QCT studies [12][13][14] based on a new potential energy surface (PES-2014) developed by our group, 12 which is a full-dimensional analytical surface fitted exclusively to high-level ab initio calculations.…”

“…The theoretical studies [6][7][8][9][10][11][12][13][14] are consistent with the experimental finding, associated with a rebound mechanism with a narrow cone of acceptance and a collinear CH 3 -H -O transition state. Recently, we reported a series of theoretical QCT studies [12][13][14] based on a new potential energy surface (PES-2014) developed by our group, 12 which is a full-dimensional analytical surface fitted exclusively to high-level ab initio calculations. These dynamics studies were performed at low, 8-20 kcal mol −1 , and high, 64 kcal mol −1 , collision energies, and reproduce the experimental data.…”

“…12 This PES-2014 gave good dynamics [12][13][14] and kinetics 23 responses, and now the effect of excitation of the C-H antisymmetric stretch mode on dynamics will be analyzed and compared with the recent experiment 21 and other theoretical results. 19,20,22 …”

Communication: Direct comparison between theory and experiment for correlated angular and product-state distributions of the ground-state and stretching-excited O(3P) + CH4 reactions

“…These PESs have recently been used for quasi-classical trajectory (QCT) and reduced-dimensional quantum dynamics computations. [7][8][9][10] In 2014 an experimental study also appeared investigating the effects of the antisymmetric stretching excitation on the angular distributions of the O( 3 P) + CH 4 (v 3 = 0, 1) reactions. 11 The experiment found that the angular distributions are backward scattered for the groundstate reaction and shift toward sideways and forward directions upon stretching excitation.…”

Perspective: Vibrational-induced steric effects in bimolecular reactions

“…30,54,55 Again, the ground-state reaction has been extensively investigated and is characterized by a direct abstraction pathway with the rebound mechanism. 35,36,[56][57][58][59][60][61][62][63] This is to be contrasted to the ground-state reaction of F + CHD 3 , for which dual mechanisms partake: a direct abstraction and a resonance-mediated pathway that prevails at lower collision energies. 38,39 Figure 3 illustrates the effects of CH stretch-excitation of CHD 3 (v 1 = 1) on the CD 3 (v = 0) product, which is the dominant product channel.…”