First Born differential cross-sections for electronic excitation in the helium atom

Generalized oscillator strengths for transitions from the ground state of the helium atom to the n(1)S, n(1)P, and n(1)D states with n < 7 are obtained from explicitly correlated wave functions. These results are used to calculate, within the first Born approximation (FBA), elastic and inelastic differential cross-sections for scattering of electrons with impact energies between 100 and 1500 eV. Detailed comparisons between FBA and measured cross-sections are presented. At small angles, the FBA is accurate over a large range of impact energies for the optically allowed transitions to the n(1)P states. The FBA reaches a comparable level of accuracy for optically forbidden transitions only at higher impact energies. The FBA is significantly in error for elastic scattering in the forward direction even at 1500-eV impact energy. (C) 2002 Elsevier Science B.V. All rights reserved.