Spectroscopic Determination of thes-Wave Scattering Length of Lithium

Two-photon photoassociation of colliding ultracold ^7Li atoms is used to probe the ^3ₔ^+ (a) ground state of ^7Li₂. The binding energy of the least-bound state of this triplet potential, 0ex{0ex}=0ex{0ex}10, is found to be 12. 470. 04 GHz. This spectroscopic information establishes that the s-wave scattering length for ^7Li atoms in the F0ex{0ex}=0ex{0ex}2, m₅0ex{0ex}=0ex{0ex}2 state is (-27. 30. 8) a₀. The negative sign of the scattering length has important implications as to whether atoms at this doubly spin-polarized state can undergo a Bose-Einstein condensation.