A SPECTROSCOPIC DETERMINATION OF SCATTERING LENGTHS FOR SODIUM ATOM COLLISIONS

We report a preliminary value for the zero magnetic field Na S-2(f = 1 , m = - 1) + Na S-2(f = 1, m = - 1) scattering length, a(1, - 1). This parameter describes the low-energy elastic two-body processes in a di lute gas of composite bosons and determines, to a large extent, the ma croscopic wavefunction of a Bose condensate in a trap. Our scattering length is obtained from photoassociative spectroscopy with samples of uncondensed atoms. The temperature of the atoms is sufficiently low th at contributions from the three lowest partial waves dominate the spec trum. The observed lineshapes for the purely long-range O-g(-) molecul ar state enable us to establish key features of the ground state scatt ering wavefunction. The fortuitous occurrence of a p-wave node near th e deepest point (R(e) = 72 a(0)) of the O-g(-) potential curve is inst rumental in determining a(1, - 1) = (52 +/- 5) a(0) and a(2,2) = (85 /- 3) a(0), where the latter is for a collision of two Na S-2(f = 2, m = 2) atoms.