Electron impact dissociation of H2and D2studied from the anticrossing signals and by the Doppler-profile technique

From the shape of the anticrossing signals induced by a motional electric field, it is possible to determine the velocities of the excited atoms produced by electron impact dissociation of H 2 and D 2 . Evidence is given for two different processes leading to 'slow' and 'fast' hydrogen (n=3 or 4) or deuterium (n=3) atoms. The 'slow' hydrogen atoms are most probably due to the predissociation of several Rydberg states of H 2 ; the 'fast' H(n=3) atoms are produced by the dissociation of repulsive states with a Franck-Condon region lying from 25 to 33 eV (+or-1 eV) and with H(1S)+H(n=3) as a limit. For the 'slow' D atoms, direct dissociation of the Rydberg states seems more important. All the conclusions of the anticrossing study are confirmed by the Doppler-profile observations. The relative population rates of the 3S, 3P and 3D levels are measured for the 'slow' H atoms.