Radiative lifetime of the2Pstate of lithium

We determine the radial dipole moment between the $2S$ and $2P$ states of atomic lithium by analyzing the long-range vibrational eigenenergies of the singly excited diatomic molecule. The result can be expressed in terms of the $2P_{\frac{1}{2}}$ radiative lifetime of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$, which is found to be 27.102(2)(7) ns. This result agrees with most current atomic-structure calculations and resolves the long-standing disagreement with previous experiment. The current level of precision is sensitive to relativistic effects in the atomic-structure calculation and to non-Born-Oppenheimer and radiation retardation effects in the molecule.