Time-independent and time-dependent photoassociation of spin-polarized rubidium

We extract information about collisions of ultra-cold ground-state rubidium atoms from observations of a g-wave shape resonance in the( 85)Rb + Rb-85 system via time-independent and time-dependent photoassociation. The shape resonance arises from a quasi-bound state inside a centrifugal barrier that enhances the excitation to the bound electronically excited state by the p hotoassociation laser in the time-independent experiment. The shape resonan ce is sufficiently long-lived that its build-up through the barrier can be observed by first depleting it via a photoassociation laser pulse and then measuring the rate of photoassociation by a second laser pulse with a varia ble delay time. A combined method of analysis of the time-independent and t ime-dependent experiments is presented. We discuss the spectroscopy of stat es of two particles with spin trapped inside a centrifugal barrier interact ing via direct and indirect spin-spin interactions.