A DPF data analysis yields accurate analytic potentials for Li 2 a 3 Σ u + and Li 2 1 3 Σ g + that incorporate 3-state mixing near the 1 3 Σ g + state asymptote
A combined-isotopologue direct-potential-fit (DPF) analysis of optical and photoassociation spectroscopy data for the a3Σu+ and 13Σg+ states of Li 2 has yielded accurate analytic potential energy functions for both states. The recommended M3LR5,38.0(3) potential for the a3Σu+ state of 7,7Li 2 has a well depth of De=333.758(7) cm-1 and an equilibrium distance of re = 4.17005(3) Å, and the associated scattering lengths are aSL = -14.759(9) Å for 7,7Li 2 and aSL = -1906(50) Å for 6,6Li 2. In spite of a gap of more than 5200 cm -1 (between v(13Σg+)=7 and v(13Σg+)=62) for which there are no data, the DPF procedure can readily yield a 13Σg+ state potential energy function that accurately represents all of the available data and smoothly bridges this gap. For 7,7Li 2 our recommended M3LR6,33.6(9) potential has a well depth of De=7093.44(3) cm, an equilibrium distance of re = 3.06514(9) Å, and its long-range tail is defined by the lowest energy eigenvalue of a 3 × 3 matrix which takes into account the 3-state mixing near its asymptote.