Electron capture from circular Rydberg atoms

Capture cross sections for circular Rydberg states have been measured as a function of the angle, φ, between ion velocity and angular momentum of the circular orbital. The system studied is 2.5 keV ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}_{}^{+}{}_{}{}^{}$ on Li(1${\mathit{s}}^2$,nlm) with n=25, l=n-1, and m=+l, where m is defined relative to a weak, external magnetic field. A strong dependence on φ is found. It is expected that studies such as the present will lead to an improved understanding of the three-body problem in the region of sufficiently large quantum numbers and impact velocities for classical physics to be accurate.