Three-dimensional quantum scattering calculations on the Cl+CH4HCl+CH3 reaction

Abstract

Reduced dimensionality quantum scattering calculations are performed on the Cl+CH₄HCl+CH₃ reaction using a rotating line umbrella (RLU) model. The breaking and forming bonds are treated explicitly as is the umbrella motion (ν₂) in CH₃ and the correlating motion (ν₄) 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 ν_3b mode of CH₄, corresponding to the breaking bond, or the ν₄ 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(ν_3b=1)→HCl(ν=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(ν_3b=1)→HCl(ν=0)+CH₃ there is predominantly backward scattering with excitation of the umbrella mode. Comparison with experimental measurements is made.