Theoretical determination of the X 2Σ+ and A 2Π potentials of CsO using relativistic effective core potentials

Theoretical potential energy curves are computed for the X ²Σ⁺ and A ²Π states of CsO using a relativistic effective core potential and a large valence Gaussian basis set. Seventeen electrons are correlated by a CI (SD ) calculation from each HF reference. We find the X ²Σ⁺ state lower by 497 and 726 cm^?1 at the HF and CI(SD) levels. Our calculated ω_e of 312 cm^?1 for the X ²Σ⁺ state agrees well with experimental values deduced from studies in matrices.