THEORETICAL SPIN-ROVIBRONIC (2)A(1)(PI(U))-(2)B(1) SPECTRUM OF THE H2O+, HDO+, AND D2O+ CATIONS

Based on extensive ab initio multiconfiguration reference configuration interaction (MRCI) electronic structure calculations, three-dimensional potential energy functions for the A2A1(II(u))-X2B1 linear/bent Renner-Teller systems of H2O+, HDO+, and D2O+ have been generated and used in beyond Born-Oppenheimer calculations of the spin-rovibronic energy levels by a variational approach. The effects of anharmonicity, rotation-vibration, electronic angular momenta, and spin coupling effects have been accounted for. For H2O+, HDO+, and D2O+ vibronic band origins for the bending levels to K(a)=5 and for selected stretching and combination levels are given. Almost all experimentally known data have been reproduced with an accuracy better than 10 cm-1 after minor modifications of the ab initio potential energy functions. Our calculated values will facilitate further experimental assignments. A consistent interpretation of the photoelectron spectra for the different isotopes of water is given. Previous assignments of the bending modes in the A2A1 state have been revised by two quantum numbers.