Measurement of fine-structure changing collision in ultracold /sup 85/Rb held in a MOT

Summary form only given. In a magneto-optical trap (MOT) two main mechanisms contribute to the total trap loss rate. Radiative escape (RE), where the spontaneous emission within the collision duration transforms internal energy into kinetic motion. Fine-structure changing collision (FSC) is an exoergic process where a pair of excited ground state atoms undergoes a change to the lower state of the fine-structure doublet, followed by a release of /spl Delta/E/sub FSC//2 in kinetic energy normally enough to eject the atoms from the trap. In earlier experiments only the total trap loss rate, which is the sum of contributions from RE and FSC, was determined. Distinguishing between these two mechanisms is important because it allows a more precise comparison with the theory, leading to a better understanding of exoergic cold collisions. In this experiment the FSC contribution to the total loss in /sup 85/Rb is measured by direct photoionization of the P/sub 1/2/ fragments.