Oscillator Strengths for the Helium Isoelectronic Sequence

Variational wavefunctions have been computed for the 1¹S, 2^{1, 3}S, 2^{1, 3}P, 3^{1, 3}P, and 3^{1, 3}D terms of ions in the helium isoelectronic sequence from He through Ne⁺⁸. The trial functions are Hylleraas type expansions, explicitly involving r ₁₂, and with expansion lengths of around 50 terms, differing slightly for the different states. Oscillator strengths have been computed for all the allowed transitions by both the dipole length and velocity formulas. Agreement between these forms, comparisons with very accurate data for neutral helium, and the accuracy of the computed energies all point to considerable reliability of the results for the entire sequence, probably around 5 percent, if not better.