Electron impact excitation of argon and krypton: improved r-ratios

Abstract

New differential cross-section ratios (r) for electron impact excitation of the metastable states of argon and krypton are presented. The new measurements are taken with improved energy resolution and a novel moveable source method which yields overall better statistical errors than earlier measurements. These measurements were taken to check the accuracy of the r-ratios observed in the earlier experiments with argon (Khakoo et al 2004 J. Phys. B: At. Mol. Opt. Phys. 37 247) which displayed significant deviations from the (statistical weight ratio) value of 5 at small scattering angles, and suggested the possibility of second-order effects in the electron impact excitation process. The measurements show that the r-ratios for argon stay close to the value of 5, in contrast to the earlier experiments, implying that second-order effects can be considered small. Additionally, new and similarly improved r-ratios for krypton were measured. These measurements reproduce the results of earlier measurements taken by our group which showed significant departures of r from the value of 5.