Collisions in an $^{85}$Rb MOT via the 5S-5D Long Range Molecular Potential

We report an enhancement of two-body collisional losses induced via a two step excitation up to the 5S-5D long range molecular potential in an $^{85}$Rb MOT. Excitation up to this state produces a flux of excited state atom pairs to close internuclear separations due to the long lifetime of this state. At these close separations, the atoms decay down to steeper potential curves, accelerating the pair out of the trap. Measurements of the loss rates as a function of laser intensities allow the identification of the loss channel involved in the collisions, and calculations of Landau-Zener avoided crossings explain the observed saturation effects. We found a two-body loss coefficient of 2.05 $\pm$ 0.06 (statistical) $\pm$ 1.0 (systematic) x 10$^{-10}$ cm$^3$/s for our conditions.