Circular polarization of the 3D state of atomic hydrogen excited by electrons

Abstract

The theory of the circular polarization from the 3²D state is analysed and angular correlation formulae are derived for the scattered n = 3 electron and the cascade Lyman-alpha radiation. The formulae include allowance for the polarization of the intermediate-state 2p electron from the LS coupling in the time evolution of the decay of the collisionally excited n = 3²D states. The effect of a finite coincidence time window is also examined. The predictions of the model are compared with the model which assumes that the intermediate-state 2p electron is unpolarized. New experimental data at an incident electron kinetic energy of 54.4 eV are reported and indicate the circular polarization of the Lyman-alpha radiation has small negative values from 10 degrees to 120 degrees . The theoretical predictions of the correlation are illustrated in a six-state close-coupling model which gives a minimum at forward angles but does not agree quantitatively with the experimental data.