VIBRATIONAL-EXCITATION OF METHANE BY 15 AND 30 EV INTERMEDIATE-ENERGYELECTRON-IMPACT

Absolute measurements of differential electron-collision cross section s have been performed for the vibrational excitation of methane in its electronic ground state at impact energies of 15 eV and, for the firs t time, at 30 eV, in the 8 degrees-95 degrees angular range. The norma lization to the absolute scale has been carried out using the inelasti c/elastic ratios and the absolute elastic differential cross section o btained from a relative flow technique recently developed in our labor atory, in which the elastic differential cross section of methane was compared to that of nitrogen at each impact energy and at each scatter ing angle. Special attention has been given to the small scattering an gular range (less than or equal to 40 degrees) where minima have been observed in the vibrational cross sections and where simultaneous inde pendent measurements have been made on two different electron spectrom eters. (C) 1997 American Institute of Physics.