Rotationally inelastic scattering and potential calculations for He + CH₄

Abstract

In two crossed beam experiments total differential and rotationally inelastic cross sections have been measured for He + CH₄ in the angular range from 3° to 70° in the c.m. system. At the low collision energy of E = 34·1 meV state resolved cross sections for the 0–3, 1–2 and 1–3 transition have been observed. All cross sections show well resolved diffraction oscillations. The inelastic cross sections are much smaller than the elastic ones. At the collision energy of E = 75·5 meV energy loss spectra have been measured, which are, at large angles, dominated by inelastic transitions. The data are compared with quantum coupled-states calculations based on a potential model of the Hartree-Fock-dispersion type, where high quality SCF-calculations are combined with damped dispersion coefficients. The gross features of the measurements are reproduced by adjusting one parameter in the damping function. However, discrepancies arise in predicting some of the inelastic cross sections at low energies.