Reduced dimensionality quantum scattering calculations on the Cl+CH4→HCl+CH3 reaction

Abstract

Reduced dimensionality quantum scattering calculations using the Rotating Line Approximation, RLA, are performed on the Cl+CH4→HCl+CH3 reaction, treating CH4 as a pseudo-diatom QH. A LEPS potential energy surface is used, where the zero-point energy of the modes not explicitly treated in the RLA calculations are included. The calculations are performed using hyperspherical coordinates and the improved log-derivative method of Manolopoulos. Boundary conditions have been applied using a hyperspherical projection method and an approximate method where the boundary conditions are applied directly in the hyperspherical coordinates. It is explicitly shown that the agreement between the methods is good. Scattering resonances are observed and related to the shape of the hyperspherical adiabats. Cumulative and state-to-state reaction probabilities are also presented. Vibrational adiabaticity is found to dominate without being exclusive. For Cl+CH4(v=1)→HCl(n=1)+CH3 and a translational energy of 0.159 eV, measured differential cross sections give predominantly forward scattering, while for Cl+CH4(v=1)→HCl(n=0)+CH3 there is predominantly backward and sideways scattering. Our calculated differential cross sections are in agreement with these general observations. Thermal rate constants have been calculated for the temperature range 200–800 K. The calculated rate constants are smaller than the experimental ones by less than 40% over the entire temperature range.