Electron correlation and the 11S→21P,31P excitation cross sections for He

Previously published values for the generalized oscillator strengths for the 1 1 S to 2 1 P and 1 1 S to 3 1 P excitations of He, calculated using non-correlated and various orders of correlated, wavefunctions, are employed to obtain total scattering cross sections for electrons, protons and hydrogen-like atoms as projectiles. Selected results for the corresponding excitations of Li + are also presented. Within the first Born approximation the behaviour of cross sections is examined as a function of the systematic introduction of electron correlation into the description of the ground-state wavefunction for the target atom. Cross sections obtained from a non-correlated wavefunction are found to be consistently too large when compared with the correlated results. The correlation trends for the scattering of atomic and non-atomic projectiles are similar in character but differ in magnitude. The use of an extensive configuration-interaction wavefunction for the 1 1 S state of He gave cross sections which agree closely with other calculations and with experiment.