Translational energy distribution and production mechanism of excited hydrogen atoms produced by controlled electron impact on H2

The Balmer-β line of the excited hydrogen atom (n=4) (Hsup(*)) produced in e-H2 collisions has been measured at a resolution of about 0.03 A and at angles of 55sup(o) and 90sup(o) with respect to the electron beam. The translational energy distribution of Hsup(*) has been calculated from an analysis of the line shape. Three major components appear and their peaks lie at about 0,4 and 8 eV. The excitation function of Hsup(*) is found to have three thresholds at 17.1, 24 and 27 eV. These results show that there are three major processes fot the formation of Hsup(*): dissociation through the (1ssigmasub(g))(4l) states of H2 and predissocation through relevant Rydberg states for the 0 eV component: dissociation mainly through the (2psigmasub(u))2 state for the 4 eV component; and dissociation mainly through the (2psigmasub(u))(4l) states for the 8 eV component. (orig.)