Generalized oscillator strengths for electronic excitation from the 2 1S and 2 3S metastable states of the helium atom

Abstract

Generalized oscillator strengths for the 2 3S– n 3S, 2 3S– n 3P, 2 3S– n 3D, 2 1S– n 1S, 2 1S– n 1P, and 2 1S– n 1D, ( n<7), transitions of helium are calculated over a large range of momentum transfers using highly accurate correlated wave functions. Unlike the case of excitations from the ground state, the generalized oscillator strengths for transitions from the metastable states have nodes. The number, location, and character of the nodes have been assessed for each transition. Inelastic differential cross-sections are calculated for 500 eV impact energy using these generalized oscillator strengths and the first Born approximation. The nodes give rise to vanishing differential cross-sections for specific scattering geometries. Total cross-sections at 500 eV are reported for each inelastic transition and compared to calculated and measured cross-sections.