EXCITATION OF HIGH VIBRATIONAL LEVELS OF H2O AND D2O BY ELECTRON-IMPACT

Vibrational excitation of H2O and D2O by electron impact to high vibra tional levels with energies up to 3 eV has been studied in the 4 eV to 10 eV incident energy range. The excitation cross sections are domina ted throughout this energy range by a broad short-lived resonance that yields excitation of two vibrational progressions that are tentativel y assigned to be predominantly (n, 0, 1) and (n, 1, 1). The B-2(1) res onance at 6.5 eV, well known in dissociative attachment, was also obse rved to yield vibrational excitation. The 2A1 resonance at 8.5 eV, als o identified in dissociative attachment, was not detected in the vibra tional excitation spectra. A spectacular interference effect was obser ved between the 'broad' and B-2(1) resonances extending over 2 eV in t he differential cross sections of higher vibrational levels. The angul ar characteristics of the interference profile lead A1 symmetry to be proposed for the 'broad' resonance. Strong isotope effects were detect ed in all the observed phenomena.