Potential curves for the ground and numerous highly excited electronic states of K-2 and NaK

Potential curves of the K-2 and NaK molecules have been computed in the framework of pseudopotential methods, over a wide range of interatomic distances. At short internuclear distances, the agreement with experimental data is excellent, the mean deviation between theoretical and experimental spectroscopic constants being 1% for the two alkali dimers. At large interatomic separation, wells and avoided crossings are observed in adiabatic potential curves of highly excited states correlated to the asymptotes close to K[4p]+K[4p] and Na[3p]+K[4p]. For example, the well depths of the (1) Sigma(+) states reach 2650 cm(-1) for K-2 and 4330 cm(-1) in the case of NaK. We demonstrate that they correspond to pseudocrossings between covalent states (dissociating into K[nl]+K[n'1'] or Na[nl]+K[n'l']) and ionic states (correlated to K++K- for K-2, Na++K-, or Na-+K+ for NaK, the negative ion being in the ground state or an autoionizing state). As for Na-2, these structures may play a crucial role in the interpretation of low-energy collisions.