Hidden Fano interferences in the resonant photoionization of He-like ions

Total and partial photoionization cross sections of positive He-like ions in their ground states have been evaluated in the vicinity of the 3(1,1${)}_3$ ${}_{}{}^1{}_{}{}^{}$ ${\mathit{P}}^0$ (‘‘3s3p’’) doubly excited state for nuclear charges ranging from Z=2 to Z=18. We observe an apparent cancellation of the Fano interferences for Z≃4–5, which results in the presence of almost Lorentzian peaks in the photoabsorption spectrum. The origin of this cancellation and the behavior of the Fano and the Starace parameters along Z are discussed.