Spectrum and decay of the doubly charged water ion

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Abstract
Ion–ion coincidence measurements on H2O, HDO, and D2O ionized by Heii light show that the main ion‐pair dissociations from low‐lying states of H2O2+ lead to OH++H+ and H++H++O. Distinct states of H2O2+ are deduced to be at 36.5±1 and at 42±1 eV above the H2O ground state. Double charge transfer measurements show two sets of singlet states of H2O2+ at 41.4 and 45 eV in agreement with the Auger spectrum. New ab initio calculations predict a vertical appearance energy of 39.2 eV for the H2O2+ ion in its 3B1 ground state, but show a very strong geometry dependence, and give an adiabatic value near 36.3 eV, in agreement with experiment.