Adiabatic interaction leading to the avoided crossing between the twin 3¹δ_g and 4¹δ_g rydberg states in na₂

We present detailed investigations of our previously reported observations of the 3¹δ_g and 4¹δ_g Rydberg states having separated-atom limits of Na(3s) + Na(4d) and Na(3s) + Na(4f), respectively, of Na2 using high-resolution cw optical-optical double resonance spectroscopic measurements and analyzing the assigned rovibrational energy levels both by the individual linear fit method and the Dunham polynomial fit method. We have sorted out e/f-parity observed energy levels, and then from the Dunham polynomial fits of the e-parity levels, we have derived molecular constants and constructed Rydberg-Klein-Rees potentials of the 31Ag and 41Ag states, which appear to be twin states with an avoided crossing at Rc = 4.10 A and a splitting of Ac = 94 cm-1. The potentials are in good agreement with the ab initio calculations and linear fit results. The A-doubling splittings and the (f-d) l-mixing are investigated. A detailed discussion is focused on the adiabatic interaction of the perturbed molecular wave functions/states causing mutual amplitude/intensity sharing giving rise to avoided crossing between the 31Ag and 41Ag states.