Electric properties of the oxonium ion in its ground and two lowest excited states

The electric dipole moments and dipole polarizabilities of the oxonium ion have been calculated for the ground and two lowest excited states from the CASSCF and CASPT2 approaches. Two basis sets — an extended ANO and a smaller segmented basis — have been compared. The best values obtained at the CASPT2 level are μ = −0.5878 au (calculated at the centre of the nuclear charges), α⊥ = 6.93 au and α∥ = 5.66 au for the ground state, α⊥ = 47.1 au and α∥ = 10.8 au for the 1A″2 excited state, α⊥ = 45.9 au and α∥ = 11.5 au for the 3A″2 excited state. To our knowledge, these are the first values available in the literature for the excited states.