Undulating Potentials of Rydberg Σ⁺-States of Me–Rg Molecules: NonEmpirical Modeling of the Na–He Exciplex

Abstract— The multireference configuration interaction method based on single and double excitations (MR–CISD), l-independent core polarization potential (CPP), and diffuse function-saturated cc-pVQZ and aug-cc-pV5Z basis sets for Na and He atoms, respectively, is used to perform nonrelativistic calculations of potential energy curves and permanent dipole moment functions for the ground and excited electronic states of the exciplex Na–He molecule up to the Na(6²S) state. The ab initio results obtained within a wide range of internuclear distances R [1.7, 20.0] (Å) quantitatively confirm the undulating behavior of interatomic potentials, predicted in the framework of the inelastic scattering theory. It is established that at large R the interatomic potentials and dipole moments of highly excited (3, 6, 10)²Σ⁺ states, converging to the Na (n = 4, 5, 6²S) + He(2²S) atomic limits, are modulated by the nodal structure of the radial Rydberg wave function (n > 3) of the s-electron of an Na atom during its scattering on a remote He atom.