Vibrational excitation of methane by positron impact: Computed quantum dynamics and sensitivity tests

We report the quantum dynamical close-coupling equations relevant for vibrationally inelastic processes in low-energy collisions between a beam of positrons and the CH₄ molecule in the gas phase. The interaction potential is described in detail and we report also our numerical technique for solving the scattering equations. The cross sections are obtained for the excitations of all the modes of the title molecule and are compared both with simpler computational approximations and with the recent experiments for the two distinct energy regions that correspond to the combined symmetric and antisymmetric stretching modes and to twisting and scissoring modes, respectively. Our calculations reproduce well the shape and the values of the experimental findings and give useful insights into the microscopic dynamics for molecular excitation processes activated by low-energy positron scattering.