Sum rules and the oscillator strength distribution in helium

Abstract

Recent experimental measurements and calculated photoabsorption cross sections for helium encompassing the discrete spectrum and continuum are tested by the sum rules S(p), p = -2, -1, 0, +1, +2. The agreement is excellent for S(-2), but degrades monotonically toward S(+2). For the latter, calculated cross sections are shown to be distinctly superior to recent experimentally derived values. The comparison of cross sections with sum rule values suggests that higher-order corrections to the latter may be useful.