Vibrational excitation of CH4by electron impact: 3-20 eV

Abstract

Differential cross sections (DCS) for the vibrational excitations ( nu 2,4, 170 meV; nu 1,3, 360 meV) of CH4 by electron impact have been investigated for incident energies of 3 to 20 eV in the range of 30 to 140 degrees using a crossed-beam apparatus. Integral and momentum transfer cross sections are calculated from the DCS. At about 7.5 eV, the angular distribution shows d-wave behaviour, and the integral cross sections are enhanced to about 10-16 cm2. The parameters of angular correlation theory with the irreducible tensor method for the T2 molecular symmetry of CH4 were obtained by fitting. It was found that the d wave alone suffices to explain the angular distributions due to the presence of a broad resonant excitation process in the nu 2,4 and nu 1,3 channels. At incident energies of 10 to 20 eV, the angular distributions are isotropic within the experimental error. At lower energies of 3 to 5 eV, the distributions are practically constant within the angular range of 40 to 140 degrees , but the cross sections continuously increase towards smaller angles.