Translational energy distribution and production mechanism of excited hydrogen atoms produced by controlled electron impact on H 2

Abstract

The Balmer-β line of the excited hydrogen atom ( n = 4) (H*) produced in e—H 2 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* 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 H* is found to have three thresholds at 17.1, 24 and 27 eV. These results show that there are three major processes for the formation of H*: dissociation through the (1sσ g)(4ℓ) states of H 2 and predissociation through relevant Rydberg states for the 0 eV component; dissociation mainly through the (2pσ u) 2 state for the 4 eV component; and dissociation mainly through the (2pσ u(4ℓ) states for the 8 eV component.