Isolated-core excitations in strong electric fields. II. Experimental results in magnesium

We report on the electron yield spectra of doubly excited magnesium atoms in electric fields in the region 50–1600 V/cm. One electron is excited to a stationary Rydberg state around n = 16, either a nonmixing state with low angular momentum or a Stark state. Subsequently the second isolated-core electron is excited with a narrow-band nanosecond laser pulse. The isolated-core excitation induces a shake-up which is measured as a function of excitation frequency. An initial low-angular-momentum state leads to a much broader shakeup than an initial Stark state, i.e., many more autoionization peaks are observed for an initial low-angular-momentum state than for an initial Stark state. Full quantum calculations introduced in the preceding paper [F. Robicheaux, preceding paper Phys. Rev. A 61, 033406 (2000)] show excellent agreement with the recorded spectra. We discuss the implications of this experiment for dielectronic recombination and compare the frequency spectra to previously reported time-dependent measurements on magnesium [J.B.M. Warntjes et al., Phys. Rev. Lett. 83, 512 (1999)].