Highly excited Rydberg states of Na2: decoupling between electronic and nuclear motion

The excited Rydberg states of Na2 are observed for very high n values up to 70. Four series nd 1Δg, nd 1Πg, nd 1Σg+, and ns 1Σg+ are identified and their quantum defects are measured. At high n values the observed spectrum is completely modified by the decoupling between the electronic angular momentum l of the Rydberg electron and the internuclear axis (l uncoupling). A perturbation model is developed to treat this phenomenon and appears sufficient to account for the main features such as interference effects in the electric dipole transition to the Rydberg series. Finally the Na2+ ion molecular constants are deduced.