Giant Cross Section for Molecular Ion Formation in Ultracold Rydberg Gases

We have studied the associative ionization of a Rydberg atom and a ground-state atom in an ultracold Rydberg gas. The measured scattering cross section is 3 orders of magnitude larger than the geometrical size of the produced molecule. This giant enhancement of the reaction kinetics is due to an efficient directed mass transport which is accelerated by the Rydberg electron. We also find that the total inelastic scattering cross section is given by the geometrical size of the Rydberg electron's wave function.