Observation of the nd Δ1 g (n=6, 7, and 8) Rydberg states of Na2 by optical-optical double resonance spectroscopy: L uncoupling and perturbations

The nd Δ1 g (n=6, 7, and 8) Rydberg states of Na2 correlating with the asymptotic limits of Na (3s) +Na (nd) have been observed using high-resolution cw optical-optical double resonance spectroscopy corresponding to the rovibrational transitions X 1 g+ (v″, J″) +h pump →B Π1 u (v′, J′) +h probe →nd Δ1 g (v,J). Totals of 104, 83, and 45 identified rovibrational e/f -parity levels in the ranges of v=0-11, 11J83; v=0-10, 11J83; and v=0-10, 11J65, have been assigned to the 6d Δ1 g, 7d Δ1 g, and 8d Δ1 g states, respectively. Using the observed quantum levels, molecular constants were determined from the Dunham fits of the e -parity levels and the Rydberg-Klein-Rees potential curves were constructed for the nd Δ1 g (n=6-8) states. The characteristics of the estimated -doubling splitting constants (q0, qv, and μ) with n (=5-8) of the nd Δ1 g series have been explored. Detailed investigations reveal that the nd Δ1 g (n=6-8) states involve L uncoupling from the internuclear axis and each of these states is affected by an asymmetric perturbation caused by the up and down adjacent states. The rotational-branch intensity and position anomalies in the observed spectra of the nd Δ1 g series (n=5-8) of Na2 lead to the conclusion that due to the effects of the L -uncoupling perturbations, the same l complexes approaching the same ion-core limits result in the same l -mixing processes which lead to the formation of the supercomplexes due to the anisotropy of the molecular-ion [Na 2+ (3s)] field. This would open up opportunities to study the effects of L uncoupling and perturbations in the nd series and high Rydberg states of other alkali dimers.