The effects of coupling to the target continuum on the electron-impact excitationof Li+

Abstract

We have investigated the effects of coupling to the continuum and highbound states on the electron-impact excitation of He-like Li+ using theRmatrix with pseudostates (RMPS) method. Previous studies onthis ion have focused on transitions from the ground state to then = 2 terms.In this work, we have determined collision strengths between all 19 terms throughn = 4.We present the results of two RMPS calculations with different numbersof pseudostates in order to study the convergence of the collisionstrengths with the size of the pseudostate expansion. In addition,we compare the RMPS collision strengths with the results of anR-matrixcalculation without pseudostates in order to determine the influence of the continuumcoupling as a function of electron energy. As one might expect, coupling to the targetcontinuum has quite large effects on the collision strengths for excitation to then = 3and 4 terms at energies above the ionization limit. However, wefind that these effects are also significant for excitation to then = 2terms and that they persist down to energies just above the excitation thresholds.The experience gained from this work will allow us to pursue similar studies inmore complex target systems. Furthermore, the results of our largest RMPScalculation provide the most complete and accurate set of excitation data for thision, which is of significant importance to research in controlled nuclearfusion.