Charge transfer and curve crossings in the [BeH2O]2+ system

Summary Diabatic and adiabatic potential energy curves have been determined for the complexation of beryllium cation with a water molecule, by means of multi-reference perturbation CI. The quasi-diabatic states correspond to Be²⁺H₂O and to nine charge transfer states (Be⁺H₂O⁺): at short beryllium-water distances the ground state is essentially Be²⁺H₂O, but at large distances several charge transfer states have lower energies. The nature of the curve crossings of the ground and lowest excited states in the [BeH₂O]²⁺ system is clarified. The changes brought about by the presence of a second water molecule are investigated.