ELIMINATION OF ELECTRON-ION PSEUDORESONANCES ASSOCIATED WITH APPROXIMATE TARGET WAVE-FUNCTIONS

One of the problems associated with close-coupling calculations of electron-impact excitation is the occurrence of nonphysical pseudoresonances. These often arise from the (N+1)-electron bound states that are routinely kept within the close-coupling expansion. Within the R-matrix formalism, we describe a transformation and reduction of the bound portion of the (N+1)-electron basis to eliminate a class of pseudoresonances associated with approximate target wave functions. In order to explain the procedure and demonstrate its effectiveness, we include a variety of examples to show how this method is capable of eliminating those resonances not attached to one of the N-electron states included within the close-coupling expansion of the target.