Translational energy distribution and production mechanism of excited hydrogen atoms produced in electron-CH 4 collisions

Abstract

The Balmer-β line of the excited hydrogen atom ( n = 4) produced in e-CH 4 collisions has been measured at a resolution of about 0.03 Å and at angles of 55° and 90° with respect to the electron beam. The translational energy distribution of H* calculated from the line shape has at least three components; the peaks in the translational energy with their threshold energies in parentheses are 3 eV (21.6 ± 0.5 eV), 0–1 eV (28.1 ± 1.0 eV) and 4 eV (35.3 ± 1.5 eV). There seems to be a fourth peak with a translational energy of about 8–12 eV. Excitation to the Rydberg states converging to the Ā 2A 1 state of CH 4 + is the major process for the formation of the first component. Optically-forbidde doubly excited states play important roles in the formation of the other components.