DIFFERENTIAL CROSS-SECTIONS FOR THE ELECTRON-IMPACT EXCITATION OF HYDROGENLIKE CARBON

We report on a study of total and differential excitation cross sections for the electron-impact excitation of hydrogenlike carbon for the transitions 1s(2)S --> 2s(2)S and 2p(2)P. These calculations have been performed for electron-impact energies ranging from 28.2 to 29.5 Ry using the close-coupling R-matrix method. This energy region has been chosen because in addition to the direct excitation of 2s and 2p, there is a sizable contribution to the excitation cross section from the doubly excited two-electron states (3l3l'), which decay predominantly to n = 2 via autoionization. Differential cross sections both for the direct nonresonant channel and in the vicinity of several autoionizing resonant states are presented. The differential cross sections in the vicinity of the autoionizing resonant states are shown to be very rich in structure. We discuss the relevance of these calculations to a recent experiment that measured the electron emission spectra for the collision of C5++H-2.