Monte Carlo random walk calculations of unimolecular dissociation of methane

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Abstract
Microcanonical rate coefficients and product energy distributions are computed for the CH3+H and CH2+H2 dissociation channels of CH4 by a random walk procedure. The formulation is based on Slater theory, but uses Metropolis Monte Carlo procedures to average over the reactant phase space. We find that the convergence rates of the calculations for the CH4 system are less rapid than that obtained in previous studies on more simple systems involving the dissociation of argon clusters. The convergence rate is found to decrease as the complexity of the process increases. Thus, convergence of the rate calculations for the simple two‐center elimination reaction to form CH3+H is found to be at least an order of magnitude faster than that for the three‐center channel leading to CH2+H2. When convergence is obtained, the computed rates and product translational energy distributions are in good accord with previously obtained quasiclassical trajectory results. The computer time required to obtain converged results for the two‐center reaction is substantially less than that needed for the corresponding trajectory calculations. It is likely that the calculations for the three‐center channel will likewise be more efficient than trajectory calculations provided importance sampling is included in the Metropolis procedure.