Predissociation of optically forbidden states in electron-hydrogen collisions as studied by coincident electron energy-loss spectroscopy

The electron energy-loss spectra of H-2 in coincidence with H(2p) formation have been measured in the range just above the dissociation limit of H(ls) + H(2p) at the incident electron energies of 30 and 150 eV and the scatter ing angle of 2 degrees, The ordinary energy-loss spectra at the same incide nt energies and scattering angle have also been measured. It is clearly see n that optically-allowed states dominate in the ordinary energy-loss spectr a while optically-forbidden states contribute noticeably to the coincident energy-loss spectrum at the 30 eV incident energy. The forbidden states pre dissociating into H(1s) + H(2p) are assigned and the branching ratio of the predissociation. the intensity ratio of the coincident energy-loss spectru m to the corresponding ordinary one, is obtained. The predissociation pathw ays into H(ls) + H(2p) from those forbidden states are discussed in detail.