Beryllium doubly excited autoionizing resonances between the2pand3pthresholds

Abstract

We present results of high resolution photoelectron spectrometry measurements for the $\ensuremath{\sigma}(2s)$ relative partial photoionization cross section between the $2p$ and $3p$ ionization thresholds in atomic beryllium. This includes the $3snp$ autoionizing resonance series converging to the $3s$ threshold, the $3pns$, $nd$ series converging to the $3p$ threshold, and several members of the $3dnp$, $nf$ series. The results for the perturbed $3snp$ series are compared with the ion yield results that give the total photoionization cross section. We found very good agreement with calculations for the $2s$ partial cross section both in the $R$-matrix approximation and a hyperspherical calculation. We confirm the perturbation of the series by the $3p4s$ interloper with a resonance profile that is the same as for the total cross section. We did not find evidence of a second interloper $(3d4p)$ between the $3s10p$ and $3s11p$ resonances. We also find very good agreement between experiment and theory for the Shore parameters of these resonances. The data for the resonances between the $3s$ and $3p$ thresholds are compared with the results of a $R$-matrix $2s$ cross section calculation. Good agreement is found for the energy positions and overall resonance shapes once the calculated energies are referred to the experimental $3p$ threshold.