Rydberg-atom-Rydberg-atom ionisation cross sections

A four-body classical-trajectory Monte Carlo method has been applied to Rydberg-atom-Rydberg-atom scattering problems. Numerical calculations were conducted over the velocity range v e /3 to 3v 2 where v 2 (au)=1/n and n is the principal quantum number of the Rydberg atom. Maximum ionisation occurs at approximately 1.25 v e with the cross sections approximately scaling as pi n 4 a 0 2 . At the lower velocities, a significant fraction of the ion production is due to negative-ion formation.