Double Electron Excitation of Lithium by Electron Impact

Abstract

Excitation of the autoionizing states caused by single inner shell electron excitations in alkalai atoms by electron impact have been well studied using various approximations. These include the Born, Glauber1 and distorted wave theories.2 In lithium, in addition to single excitation, there have been some doubly excited states observed. The doubly excited states with the two electrons are the most fundamental atomic species which autoionize. Such doubly excited states in helium and alkaline earths have also been studied.3-5 A first step towards the study of such excitations in lithium would be to find the cross sections for their production by electrons. The first calculations of this nature were done by Kulander and Dahler4 using the simple Born Oppenheimer approximation. They reported results for Li(1s)2(2s)2S→Li(1s) (2p)2 4P. We reconsidered this problem in a more precise manner using the distorted wave theory. Our distorted wave calculation includes distortion of the initial and final states of the incoming and outgoing electrons separately by using different distorting potentials. We have used the static potential, the polarization of the target lithium atom as well as the exchange of the incoming electron with the bound electrons in the target. The bound states of the target are represented in initial and final states by the Hartree Fock wave functions as used by Kulander and Dahler.4 The details of the analysis, results and discussion will be presented at the conference. In Table I we briefly display our results using various versions of the distorted wave theory (Ei is the incident energy in Ry, I and F represent the inclusion of the initial and final state static potentials respectively, E and P signify the additional inclusions of the exchange and polarization potentials).