The Li2 F 1Σg+ 'shelf' state: Accurate potential energy curve based on the inverted perturbation approach

We report an accurate inverted perturbation approach (IPA) potential energy curve for the “shelf” F 1Σg+ state in Li2 which reproduces positions of the experimental energy levels available in the literature for all three isotopomers 7Li2, 6Li7Li, and 6Li2 with a standard deviation of 0.11 cm−1. Our analysis significantly improves the shape of the recently reported Rydberg–Klein–Rees (RKR) potential curve of the F 1Σg+ state [Antonova et al., J. Chem. Phys. 112, 7080 (2000)] and provides evidence for the existence of a shallow minimum in the shelf region. Using our IPA potential curve we were able to localize and identify some local perturbations in the spectra, as well as to correct the assignment of several spectral lines previously observed experimentally.