Observation of perturbed3snpdouble photoexcited Ryberg series of beryllium atoms

Abstract

We observed the $3snp$ autoionizing Rydberg series of the Be atom in order to investigate the double-photoexcitation processes in two-$s$-electron systems. We employed synchrotron radiation to photoexcite the Be atoms and measured the generated ${\mathrm{Be}}^{+}$ photoions by the time-of-flight method. The $3snp$ $(n=3\text{--9})$ photoexcitation resonance peaks with interloper state of $3p4s$ that converges to ${\mathrm{Be}}^{+}(3p)$ threshold were observed. We derived the resonance parameters of $3snp$ series from a fitting procedure and obtained the Fano parameter $q$, energy position ${E}_{0}$, and resonance width $\ensuremath{\Gamma}$. These parameters are in good agreement with theoretical values. In the vicinity of the $3s5p$ state these experimental results clearly revealed the influence of the interloper $3p4s$ state, and the comparison with the numerical calculations indicates that more detailed calculations might be required to fully explain this phenomenon.