Photoionization from 1sns1,3Sestates of helium

We present theoretical photoionization cross sections from the 1sns ${}_{}{}^{1,3}{}_{}{}^{}$ ${\mathit{S}}^{\mathit{e}}$ bound excited states of the helium atom based on a configuration-interaction procedure for the continuum, using a finite ${\mathit{L}}^2$-basis set constructed from a nearly complete set of B-spline-based one-particle hydrogenic orbitals. In addition to the nonresonant spectra near the first ionization threshold, resonant structures associated with selected sp,2${\mathit{n}}^{\pm }$ and 2pnd ${}_{}{}^{1,3}{}_{}{}^{}$ ${\mathit{P}}^{\mathit{o}}$ autoionization series below the ${\mathrm{He}}^{+}$ N=2 threshold are examined in detail. The widths and resonance energies of all ${}_{}{}^{1,3}{}_{}{}^{}$P autoionization series are also reported and compared with other available theoretical and experimental results.