We determine the energies of twelve vibrational levels lying within 20
GHz of the lowest dissociation limit of Rb-85(2) with two-color photo
association spectroscopy of ultracold Rb-85 atoms. The levels lie in a
n energy range for which singlet and triplet states are mixed by the h
yperfine interaction. We carry out a coupled channels bound state anal
ysis of the level energies, and derive accurate values for Rb-85(2) in
teraction parameters. The information obtained is sufficient to allow
for quantitative calculations of arbitrary Rb ultracold collision prop
erties.