Theoretical Study of the Complex-Forming CH + H₂ → CH₂ + H Reaction

Abstract

The complex-forming CH + H2 --> CH2 + H reaction is studied employing a recently developed global potential energy function. The reaction probability in the total angular momentum J = 0 limit is estimated with a four-atom quantum wave packet method and compared with classical trajectory and statistical theory results. The formation of complexes from different reactant internal states is also determined with wave packet calculations. While there is no barrier to reaction along the minimum energy path, we find that there are angular constraints to complex formation. Trajectory-based estimates of the low-pressure rate constants are made and compared with experimental results. We find that zero-point energy violation in the trajectories is a particularly severe problem for this reaction.

Capture approximations beyond a statistical quantum mechanical method for atom-diatom reactions

“…The difference becomes even more remarkable when the system under study gets more demanding in terms of numerical effort. Preliminary investigations on reactions such as Si+OH reveals that several months One of the most interesting applications of these approaches could be the framework of more complicated systems such as four atoms collisions [24]. AB+CD or A+BCD reactions constitute an ideal scenario to employ approximations which may help to simplify the calculations.…”

Quantum Mechanical Capture/Phase Space Theory Calculation of the Rate Constants for the Complex-Forming CH + H2 Reaction

“…We employ the same potential energy function that was used in Paper I. 3 However, the only portion of the potential relevant to these calculations is the entrance channel. Thus, calculations of this type do not require a global potential energy surface, simply that the entrance channel be well characterized.…”

“…[1][2][3] Consequently, there have been numerous experimental and theoretical studies of this system. [1][2][3][4][5][6][7][8][9] Reaction (R1) is a barrierless, endothermic reaction with ∆H 0 (0 K) ) 0.145 ( 0.006 eV, whereas ∆H 0 (0 K) ) -4.592 ( 0.003 eV for (R2). 3 In a previous work 3 (hereafter, Paper I), we carried out quasiclassical trajectory (QCT) and quantum wavepacket calculations on the forward reaction (R1) consistent with the low ("zero") pressure gas phase limit where (R2) is not relevant.…”

“…[1][2][3][4][5][6][7][8][9] Reaction (R1) is a barrierless, endothermic reaction with ∆H 0 (0 K) ) 0.145 ( 0.006 eV, whereas ∆H 0 (0 K) ) -4.592 ( 0.003 eV for (R2). 3 In a previous work 3 (hereafter, Paper I), we carried out quasiclassical trajectory (QCT) and quantum wavepacket calculations on the forward reaction (R1) consistent with the low ("zero") pressure gas phase limit where (R2) is not relevant. These calculations used a global potential energy surface that incorporated very high level ab initio electronic structure information.…”

Real wavepacket code for ABC+D→AB+CD reactive scattering

“…These approximations considerably reduce the effort associated with estimating observables such as cross sections and rate constants that involve summations over many total angular momenta. HD-RWP calculations have also been reported for several AB + CD → ABC + D tetratomic reactions, including the OH + H 2 [15], OH + D 2 [16], OH + CO [17], and CH + H 2 [18] systems. Owing to the computational challenges of such calculations, several parallel-computing strategies for carrying out RWP calculations have also been developed [19][20][21].…”