We observe bound states just below the dissociation limit and shape and Feshbach resonances between the ground state hyperfine asymptotes by Raman spectroscopy on a molecular beam of sodium dimers. The rotational selectivity of a two-photon transition gives access to specific states of nuclear motion and thus to cold collision properties of two colliding atoms. Modeling of the collisional resonance structures requires a multichannel treatment of the nuclear dynamics that uses highly accurate X 1 ⌺ g ϩ and a 3 ⌺ u ϩ potentials. These potentials are constructed from bound levels just below the ground state asymptote measured in this experiment and bound state information available in the literature. We also present simulations of the spectrum between the ground state hyperfine asymptotes. The good agreement shows that accurate potentials obtained from bound state information are able to reproduce scattering properties of two colliding sodium atoms. From this analysis we find for the scattering lengths a( f ϭ2)ϭa 1,Ϫ1 ϭ52.98(40)a 0 , a singlet ϭ19.20(30)a 0 , and a triplet ϭ62.51(50)a 0 , where 1a 0 ϭ0.052 917 7 nm.

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We report on atom optical experiments employing a magnetooptical trap as a source of a pulsed beam of slow atoms. After turning off the trap, experiments are performed on the cloud of atoms in free fall over a distance of 45 cm. We give a detailed description of the apparatus and discuss experimental results on the diffraction of atoms from a standing light wave in the regimes of short, intermediate and long interaction times.PACS: 03.75Be, 32.80Pj, 42.50Vk.

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