Photoionization cross section of helium for photon energies 59-67 eV: The(sp,2n+)Po1Rydberg series of autoionizing resonances

The central position of the $2s2p {}_{}{}^1{}_{}{}^{}P_{}^o{}_{}{}^{}$ two-electron resonance of He at 206.21 Å has been remeasured using the background continuum of the National Bureau of Standards storage ring facility. In addition, the line-shape parameter $q$ and width $\Gamma$ of the resonance have also been obtained. We obtained a value of 60.151 ± 0.010 eV for the resonance position, -2.6 ± 0.3 for the line-shape parameter, and 0.038 ± 0.002 eV for the width of the resonance. Our value for the resonance position is in good agreement with the theoretical calculation of 60.145 eV of Bhatia and Temkin and lies within the error budget of the previous experimental measurements of Madden and Codling. Parameter values for the other resonances have also been obtained and are in good agreement with the earlier measurements of Madden and Codling.