Ab initio potential energy surface and vibrational energies of Li3−

An ab initio quantum mechanical study of the potential energy surface of Li3− has been carried out. The potential energy surface, obtained via a quantum configuration interaction calculation using single and double substitutions plus perturbatively obtained triples, on a [11s,3p,1d; 6s,3p,1d] basis set predicts the ground electronic state (1Σg+) to be linear (D∞h) with a LiLi separation of 3.03 Å at the equilibrium geometry. The surface has been fitted using a multi-dimensional least-squares procedure and has been embedded in a recently developed Eckart-Watson Hamiltonian. The low-lying vibrational band origins of Li3− have been calculated using a variational approach and rectilinear displacement coordinates.