Three-dimensional quantum scattering calculations on the Cl+CH4⇆HCl+CH3 reaction

Reduced dimensionality quantum scattering calculations are performed on the Cl + CH4 reversible arrow HCl + CH3 reaction using a rotating line umbrella (RLU) model. The breaking and forming bonds are treated explicitly as is the umbrella motion (v(2)) in CH3 and the correlating motion (v(4)) in CH4. A potential energy surface, where the zero-point energy of the modes not explicitly treated in the scattering calculations are approximately included, has been constructed from a surface for CH4, due to Hase and collaborators, and an LEPS function, treating the reactive bonds. The calculations are carried out using a log-derivative propagation method in hypercylindrical coordinates. A single-sector hyperspherical projection method has been developed for applying boundary conditions. The forward reaction rate is enhanced by placing one quantum either in the v(3b) mode of CH4, corresponding to the breaking bond, or the v(4) mode. The reverse reaction is enhanced by placing one quantum in the HCl vibration but is impeded by placing a quantum in the CH3 umbrella mode. For Cl + CH4(v(3b) = 1) --> HCl(v = 1) + CH3 and a translational energy of 0.159 eV, calculated differential cross-sections give predominantly forward and sideways scattering without excitation of the umbrella motion of CH3. For Cl + CH4(v(3b) = 1) --> HCl(v = 1) + CH3 there is predominantly backward scattering with excitation of the umbrella mode. Comparison with experimental measurements is made.