Ionization Cross Sections for Rydberg-Atom-Rydberg-Atom Collisions

Abstract

A classical-trajectory Monte Carlo method has been applied to collisions of two Rydberg atoms. Numerical calculations were made for velocities $v=0.01\mathrm{}{v}_e \mathrm{to} 10v_e$, where the Rydberg electron's velocity $v_e(\mathrm{a}.\mathrm{u}.\mathrm{})=\frac{1}{n}$ and $n$ is the principal quantum number of the Rydberg atom. The total ionization cross sections scale as $n^4$ and show a $v^{-0.65\mathrm{}}$ dependence at low $v$, a slight maximum around $v_e$, and a rapid decrease at high $v$. The cross sections are almost an order of magnitude larger than $\pi n^4{a_0}^2$ at thermal energies.