SUM-RULES AND THE OSCILLATOR STRENGTH DISTRIBUTION IN HELIUM

Recent experimental measurements and calculated photoabsorption cross sections for helium encompassing the discrete spectrum and continuum a re 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 t he latter, calculated cross sections are shown to be distinctly superi or to recent experimentally derived values. The comparison of cross se ctions with sum rule values suggests that higher-order corrections to the latter may be useful.