Dissociative excitation of water molecule by electron impacts, 1

Emission cross sections are evaluated in the Born approximation for the dissociative excitation processes of H2O by electron impacts, accompanied by the OH violet band, or the Lyman-α emission. Wave functions are from the Hatano-Nomura-Tanaka basis set as well as the Lin-Duncan set. The choice of wave functions strongly affects the magnitude of the cross section, but hardly affects its dependence on the incident electron energy. For the OH band, main contribution comes from the transition 3a1 → 4a1, and the electron exchange collision should be considered. For the Lyman-α emission, to which a number of superexcited states may correlate, it is found that the contribution of the transition 1b2 → 6a1(=4sa1) is dominant, while ones of 1b2 → 3da1, 3da2 and 3db2 the next. The calculated cross section is different from the experimental one at low energies of the incident electron, but is in accord with the experimental one at high energies. Alternative comparison is made on the optical and the generalized oscillator strengths. (auth.)