Accurate analytic potentials for $Li2(XΣ1g+)$ and $Li2(AΣ1u+)$ from 2 to 90 Å, and the radiative lifetime of $Li(2p)$

Extensions of the recently introduced “Morse/long-range” (MLR) potential function form allow a straightforward treatment of a molecular state for which the inverse-power long-range potential changes character with internuclear separation. Use of this function in a direct-potential-fit analysis of a combination of new fluorescence data for $L7,7i2$⁠, $L6,6i2$⁠, and $L6,7i2$ with previously reported data for the $A(Σ1u+)$ and $X(Σ1g+)$ states yields accurate, fully analytic potentials for both states, together with the analytic “adiabatic” Born–Oppenheimer breakdown radial correction functions which are responsible for the difference between the interaction potentials and well depths for the different isotopologues. This analysis yields accurate well depths of $De=8516.709(±0.004)$ and $8516.774(±0.004)cm−1$ and scattering lengths of $18.11(±0.05)$ and $23.84(±0.05)Å$ for the ground-states of $L7,7i2$ and $L6,6i2$⁠, respectively, as well as improved atomic radiative lifetimes of $τ(2p)=27.1018(±0.0014)ns$ for $L7i(2p)$ and $27.1024(±0.0014)ns$ for $L6i(2p)$⁠.