Measurements of partial cross sections and autoionization in the photoionization of helium toHe+(N=2)

We have measured the partial cross sections for ionizing neutral helium to ${\mathrm{He}}^{+}$ in the $2s$ and $2p$ levels from threshold to 130 eV. Near threshold the data favor the close-coupling calculations of Jacobs and Burke rather than the many-body calculations of Chang, in contrast to the total $N=2\mathrm{}$ cross section. We have also made a detailed study of the autoionizing resonances leading to the $N=3\mathrm{}$, $N=4\mathrm{}$, and $N=5\mathrm{}$ thresholds. We present resonance parameters for the $N=3\mathrm{}$ series. The energies of the resonances agree well with calculated and experimental values, but the widths show substantial disagreement with calculations.