Theoretical spectroscopic data of the HO2+ ion Original Research Article

Quartic force fields, spectroscopic constants, and vibrational energies were obtained from three-dimensional potential energy functions (PEFs) calculated using the multi-reference internally contracted CI approach for the 2A′′ ground state of the neutral HO2 molecule and the three lowest electronic states, X3A′′, A1A′ and B1A′′ of the HO2+ ion. In the X2A′′ and A1A′ states the OO stretching mode lies below the OOH bending mode, but in the deuterated species their order changes and the OO stretch is shifted to higher energies. In X3A′′ and B1A′′ the OO stretching mode lies in both isotopomers above the bending mode. For the electronic ground state of the ion following rotational constants and anharmonic wavenumbers were obtained: Ae=21.393, Be=1.270, Ce=1.1988; ν1=3066, ν2=1361 and ν3=1071 (all values in cm−1). The first excited singlet state 1A′ is calculated to lie 1185 cm−1 above the triplet ground state. Its vibrational states are embedded in the electronic ground state. The barrier for the proton migration in the X3A′′ state has a T-shaped structure and lies as high as 12970 cm−1 above its minimum, but still below the first dissociation asymptote. Singlet-triplet crossings and the conical intersection regions on the PEFs of the charge transfer reaction O2+H+ → O2++H have been located.