Observation of autoionizing resonances in core electron shakeup spectra

New phenomena observed in the shakeup satellite electron spectrum Ne 1s are discussed. It is shown that for satellites lying above the shakeoff threshold, the structures observed correspond to autoionizing resonances. By use of high-resolution x-ray photoelectron spectroscopy the Fano profile of the 2s-3s lower shakeup satellite line is resolved for the first time. The Fano parameters for this line are determined to q=-2.2(2) and ρ²=0.35(5). The width of the resonance is 0.57(7) eV, i.e., almost a factor of 2 larger than the unperturbed linewidth.