Theoretical investigations of the reaction dynamics of polyatomic systems: Chemistry of the hot atom (T* + CH4) and (T* + CD4) systems

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Abstract
An unadjusted computation of the reaction dynamics in the (CH4 + T*) and (CD4 + T*) systems has been carried out. The six‐body potential‐energy surface has been obtained from the equilibrium thermodynamic and spectroscopic data for reactants and products, the results of all‐valence electron INDO and all‐electron, ab initio SCF and CI quantum calculations, and previously formulated three‐ and four‐body valence‐bond (VB) potential surfaces. The computed saddle‐point geometries for axial abstraction and inversion displacement are in good to excellent agreement with previous ab initio CI calculations. The saddle‐point energies are in fair to good agreement. Computed fundamental vibration frequencies for CH4 are in excellent accord with ir and Raman data. Reaction cross sections as a function of relative translational energy for abstraction, displacement, and fragmentation in (CH4 + T*) and (CD4 + T*) systems have been computed by quasiclassical trajectory analysis. Calculated thresholds are in quantitative agreement with experiment. The abstraction and displacement reaction dynamics are examined and discussed. Hot‐atom yield ratios in both systems have been determined through solutions of the integral reaction probability equation. Computed results for nuclear recoil tritium incident upon CH4 are in quantitative agreement with experiment. Yield ratios for [CD3T/DT] obtained by photolysis of TBr are in excellent accord with experiment at all photolysis energies. Abstraction yields in CH4 are computed and found to be in good agreement with experiment. The low energy (40–65 kcal/mole) displacement cross sections are found to be too low by a factor of 2–3.