Fluorescence excitation spectra of OH(A), OH(B), OH(C), Lyman α, Balmer α, Balmer β, and H2O+(Ã) are recorded in H2O in the 9–35 eV photon excitation range. The OH(A) fluorescence quantum yield is measured from 9.2 to 13.6 eV incident photon energy. The pressure dependence of the H2O+(Ã) fluorescence excitation spectrum is investigated and the quenching rate constant of H2O+(Ã) by H2O is found to be equal to (4±2)×10−10 cm3 s−1. New Rydberg states are observed: a continuum-like state in the 10–12.6 eV range assigned to the (3a1)−1 (3pb2) 1B2 state and two broad bands lying at 27–29 and 30–32 eV, respectively, assigned to Rydberg states converging towards the (2a1)−1 innervalence state of H2O+. The valence character of the nsa1 Rydberg states is discussed. The decay processes of valence-type vs pure Rydberg states are investigated. All energetically accessible dissociation channels producing fluorescent fragments are observed and the fragments appear at their thermodynamical threshold. The competition between autoionization and dissociation into neutrals is shown to occur only for pure Rydberg states. Possible dissociation mechanisms are discussed.

Imaging and time-resolved coincidence techniques are combined to determine ion-electron (v-->(i),v-->(e)) velocity correlations in dissociative photoionization of diatomic molecules induced by synchrotron linearly polarized light P-->. The (v-->(i),v-->(e), P-->) vector correlation yields the identification of each process, together with the ( straight theta(e), straight phi(e)) electron emission in the molecule frame for each orientation of the internuclear axis with respect to the polarization. Strong electron emission anisotropies are observed in the NO molecule frame for the parallel and the perpendicular transitions of the NO+hnu(22-25 eV)-->NO+(c(3) Pi)+e-->N+(3P)+O(3P)+e reaction.