Collisional energy transfer between Rydberg and ground-state atoms

The absolute cross section for the energy transfer between the nP Rydberg atom (n=35–60) and the ground-state (5S) atom of rubidium is measured to be 4.8×${10}^2$ A${̊}^2$ for thermal collisions at 420 K. This value of the cross section is in agreement with the calculated value for resonant charge transfer at the relevant collision energy. It is concluded that the energy transfer process is essentially charge transfer between the Rydberg ion core and the ground-state atom, where the Rydberg electron stays as a spectator.