Properties of Cold Collisions of

We have determined properties of cold 39 K + 39 K and 41 K + 41 K collisions by a multichannel Inverted Perturbation Approach applied to spectroscopic data of highly-excited 39 K singlet and triplet bound states. We predict positive scattering lengths for the 39 K + 39 K and 41 K + 41 K singlet potentials, as well as for the 41 K + 41 K triplet potential, and a negative value for 39 K + 39 K triplet scattering. From a study of the magnetic field dependence we conclude that 41 K may be the first example of an alkali species with a Feshbach resonance in the magnetic field range where these atoms can be trapped in the f = 1; m f = \Gamma1 hyperfine state, thus providing a possibility to switch between stable and instable condensates in a Bose-Einstein condensation experiment. Typeset using REVT E X The recent observation of Bose Einstein condensation (BEC) in weakly-interacting atomic gases of rubidium [1], lithium [2] and sodium [3] is an important step tow..