Experimental Investigation of Ultracold Atom-Molecule Collisions

Ultracold collisions between Cs atoms and Cs₂ dimers in the electronic ground state are observed in an optically trapped gas of atoms and molecules. The Cs₂ molecules are formed in the triplet ground state by cw photoassociation through the outer well of the 0_g^-(P_3/2) excited electronic state. Inelastic atom-molecule collisions converting internal excitation into kinetic energy lead to a loss of Cs₂ molecules from the dipole trap. Rate coefficients are determined for collisions involving Cs atoms in either the F=3 or F=4 hyperfine ground state, and Cs₂ molecules in either highly vibrationally excited states (v^′=32–47) or in low vibrational states (v^′=4–6) of the a ³Σ_u⁺ triplet ground state. The rate coefficients β∼10^-10  cm³/s are found to be largely independent of the vibrational and rotational excitation indicating unitary limited cross sections.