EXAMINATION OF THE STRUCTURE, LAMBDA-DOUBLING, AND PERTURBATIONS IN THE 1-1-PI-G STATE OF LI2

Fluorescence in the C1Πu-11Πg and 21Σu+-11Πg transitions of 7Li2 and 6Li2, excited by ultraviolet lines of argon and krypton ion lasers, has been examined at high resolution in the region 7000-12 000 cm-1 using a Fourier transform spectrometer. The analysis has provided molecular constants for the 11Πg state which are isotopically consistent and in good agreement with ab initio predictions. An RKR potential curve, extending to rmax = 24 A ̊, has been constructed. The dissociation energy, calculated by several methods using long-range analysis, is found to be 1422.03 ± 0.05 cm-1 and the long-range terms in the potential energy expansion are C3 = 1.805(10) × 105 cm-1 A ̊3 and C6 = 7.77(60) × 106 cm-1 A ̊6. The precision in determining De(11Πg) has allowed us to lower the error limits on the ground state dissociation energy to 0.10 cm-1 (De(X1Σg+) = 8516.78(10) cm-1). The interaction between the 11Πg and 21Σg+ states is studied in detail and is shown to account for all the irregularities observed in the 11Πg state Λ doubling and for the strong perturbations that are observed. The detailed study of the interaction and the intensities of transitions to the perturbed levels has led to the determination of electronic transition moment ratios for the 21Σu+-11Πg and 21Σu+-21Σg+ transitions and shown that they are in accord with ab initio calculations. © 1990.