Doubly excited states of water in the inner valence range

The cross sections for the emission of dispersed fluorescences in the ultraviolet and visible ranges by excited hydrogen atoms, OH radicals and OH+ fragment ions produced in the photoexcitation of H2O have been obtained as a function of incident photon energy in the range 17–41 eV, in which four superexcited states have been found. Two of these states around 25 and 28 eV are doubly excited states, which have been investigated in detail for the first time, and the others are single-hole one-electron superexcited states around 19 and 31 eV. It is remarkable that the doubly excited states around 28 eV give the oscillator strengths for Balmer fluorescences comparable to those given by the nearby single-hole one-electron states around 31 eV that are built on the (2a1)−1 ion core, which seems not to be amenable to the independent electron model. The state-resolved isotope effect on the oscillator strengths for Balmer-α fluorescence in H2O and D2O has been revealed. An overview of the doubly excited states of CH4, NH3 and H2O has been given in terms of the oscillator strengths for Balmer fluorescences and their energies based on the present investigation and preceding ones by Kato et al (2002 J. Phys. B: At. Mol. Opt. Phys. 35 4383 and 2003 J. Phys. B: At. Mol. Opt. Phys. 36 3541).