Multistep excitation of autoionizing states of neutral strontium

Resonance profiles of the lowest members of the Sr 5pns and 5pnp autoionizing series have been measured using the two- or three-step excitation schemes. Interference between different excitation pathways is manifested as the Beutler-Fano asymmetric profile in the two-step excitation but is absent in the three-step isolated-core-excitation schemes. These spectra are characterized by either Lorentzian or Fano profile. The manifestations involved in the observed spectra are interpreted in detail. The scaled widths of different autoionizing series are compared.