SPECTROSCOPIC DETERMINATION OF THE S-WAVE SCATTERING LENGTH OF LITHIUM

Two-photon photoassociation of colliding ultracold 7Li atoms is used to probe the u+3(a) ground state of 7Li2. The binding energy of the least-bound state of this triplet potential, =10, is found to be 12.47 0.04 GHz. This spectroscopic information establishes that the s-wave scattering length for 7Li atoms in the F=2, mF=2 state is (-27.3 0.8)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. © 1995 The American Physical Society.