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 investigate the influence of a laser field, which is near-resonant to the atomic sodium 3 2 P 1/2 → 3 2 D 3/2 transition, on the last bound levels of the A 1 Σ + u state in Na2. In a molecular beam experiment level shifts up to ≈ 100 MHz and light induced line broadenings were observed using an optical double resonance excitation scheme. Moreover, the coupling laser can reduce the number of bound levels of the A state by one or more units, which effectively means that in the picture of a collision of a 3 2 S 1/2 and a 3 2 P 1/2 -atom the scattering phase is altered by more than π. The observed effects are interpreted as light induced couplings of the A 1 Σ + u state, which correlates to the 3s 1/2 +3p 1/2 asymptote, to the 4 1 Σ + g and 2 1 Πg states at the 3s 1/2 +3d 3/2 asymptote. We performed multi-channel calculations, applying the mapped Fourier grid method, which reproduce our experimentally observed level shifts well.PACS. 34.50.Rk Laser-modified scattering and reactions -33.80.-b Photon interactions with molecules -42.62.Fi Laser spectroscopy

The filtered laser excitation technique was applied for measuring transition frequencies of the Ca2 B-X system from asymptotic levels of the X 1 Σ + g ground state reaching v ′′ = 38. That level has an outer classical turning point of about 20Å which is only 0.2 cm −1 below the molecular 1 S+ 1 S asymptote. Extensive analysis of the spectroscopic data, involving Monte Carlo simulation, allowed for a purely experimental determination of the long range parameters of the potential energy curve.The possible values of the s-wave scattering length could be limited to be between 250a0 and 1000a0.