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

Vibrational excitation of H2O and D2O by electron impact to high vibrational 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 dominated throughout this energy range by a broad short-lived resonance that yields excitation of two vibrational progressions that are tentatively assigned to be predominantly (n, 0, 1) and (n, 1, 1). The B-2(1) resonance at 6.5 eV, well known in dissociative attachment, was also observed to yield vibrational excitation. The 2A1 resonance at 8.5 eV, also identified in dissociative attachment, was not detected in the vibrational excitation spectra. A spectacular interference effect was observed between the 'broad' and B-2(1) resonances extending over 2 eV in the differential cross sections of higher vibrational levels. The angular characteristics of the interference profile lead A1 symmetry to be proposed for the 'broad' resonance. Strong isotope effects were detected in all the observed phenomena.