Experimental study of cold collision between metastable Krypton and Rubidium atoms

The collision between atoms and molecules is one of the major research fields in atomic and molecular physics. The advancement of laser cooling, Stark deceleration and other manipulation methods has enabled studies of the atomic (molecular) collision at low temperature (<1 K). Under such conditions, the collision process is dominated by just a few partial waves. Therefore, it provides a good playground to observe some quantum phenomena, such as shape resonance, etc..

Here we report on a cold collision experiment between metastable Kr (Kr*) and Rb atoms. Our approach combines laser trapping and manipulation with velocity mapping imaging (VMI) techniques. The Kr* atoms are first loaded into a Magneto-Optical Trap (MOT). To study the Kr*-Rb ionization reaction, the cold Kr* atoms are launched toward Rb atoms in the ground state by a moving molasses with a controlled collision energy. The ion products produced at the center of the collision region are analyzed with a VMI system. Rb-Kr* reaction cross-sections between 15 mK to 3 K are measured. We observed pronounced dependence of the reaction cross-section on collision energies. The most notable feature is that the reaction is suppressed at the collision energy about 125 mK, which could be a result of interference between different partial waves or formation of molecular superexcited states. Comparison between experiments and high precision quantum chemistry calculations in the future may shed more lights on the dynamics of the cold Rb-Kr* collision process.