target states are represented using a full configuration interaction treatment within a basis of Slater-type orbitals optimized to give accurate vertical excitation energies. Results are presented for eigenphase s u m , in which the resonant and other features are analysed, as well as total electronic excitation cross sections. Extensive comparison is made with the available experimental data. In contrast to many previous ab initio calculations our results are in good agreement with the observed electronic excitation cross sections for all the processes considered. 0953-4075/90/244625+15$03.50 @ 1990 IOP Publishing Ltd 'feature' 'c'/'e' 1 4 2 ~~2 ~~ , , c / e ' I 1 o i 2 4 2 a ; 'feature' 'feature' 'd' 10:27ri20i ? 'resonance' 'resonance' Of course it is cross sections rather than eigenphase sums which are observed experimentally. Figures 6 to 11 present our total cross sections for electronic excitation