The ejected-electron spectra arising from the decay of the 4p nln l n l 5 ¢ ¢   autoionizing states in Sr atoms have been studied precisely at the incident-electron energies close to excitation and ionization thresholds of the 4p 6 subshell. The excitation behaviors for 58 lines observed between 12 and 21eV ejected-electron kinetic energy have been investigated. Also, the ab initio calculations of excitation energies, autoionization probabilities and electron-impact excitation cross sections of the states 4p nln l n l 5 ¢ ¢   (nl = 4d, 5s, 5p; n l ¢ ¢ = 4d, 5s, 5p; n l   = 5s, 6s, 7s, 8s, 9s, 5p, 6p, 5d, 6d, 7d, 8d, 4f, 5g) have been performed by employing the large-scale configuration-interaction method in the basis of the solutions of Dirac-Fock-Slater equations. The obtained experimental and theoretical data have been used for the accurate identification of the 60 lines in ejected-electron spectra and the 68 lines observed earlier in photoabsorption spectra. The excitation and decay processes for 105 classified states in the 4p 5 5s nl 2 , 4p 5 4d nl 2 and 4p 5 5snln l ¢ ¢ configurations have been considered in detail. In particular, most of the states lying below the ionization threshold of the 4p 6 subshell at 26.92eV possess up to four decay channels with formation of Sr + in 5s 1 2 , 4d 3 2,5 2 and 5p 1 2,3 2 states. Two-step autoionization and two-electron Auger transitions with formation of Sr 2+ in the 4p 6 S 1 0 ground state are the main decay paths for high-lying autoionizing states. The excitation threshold of the 4p 6 subshell in Sr has been established at 20.98±0.05eV.

The ionization of Mg 3s and 2p and He 1s has been studied in (e, 2e) experiments at about 1000 eV incident energy and 20 eV ejected electron energy for a momentum transfer between 0.5 and 2.1 au. The comparison with the predictions of the distorted wave Born approximation model shows a generally good agreement between experiment and theory. The differences observed between the He and Mg angular distributions can be explained as an initial state effect and are attributed to the differences between the He 1s and Mg 3s wavefunctions in the momentum space.

The excitation cross-sections for the 5p55d6s2 autoionizing states of Ba atoms are studied experimentally and theoretically in an electron-impact energy range from the excitation thresholds of the states up to 600 eV. Experimental data are obtained by determining the intensities of lines in the ejected-electron spectra measured at an observation angle of 54.7∘. The incident-electron and ejected-electron energy resolutions are 0.2 eV and 0.07 eV, respectively. The calculations are performed in the distorted wave approximation by using relativistic radial wave functions obtained in the standard Dirac–Fock–Slater method. For all the states, the experimental cross-sections reach their maxima at low impact energies revealing by that predominantly the spin-exchange character of the excitation of autoionizing states. The structure of the near-threshold maxima indicates the formation of strong negative-ion resonances. At high impact energies, the shape and value of the cross-sections are determined by configuration and state mixing effects.

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The 4p6 excitation-autoionization (EA) cross-section of Sr atoms has been measured at electron-impact energies from the threshold to 600 eV. The cross-section has a pronounced resonance character in the near-threshold region, reaching its maximum value of (2.5 ± 0.8) × 10−16 cm2 at 24.5 eV. The shape and absolute value of the cross-section are determined by the excitation dynamics and the decay mode of autoionizing states from 4p54d5s2, 4p54d2nl and 4p54d5snl configurations. A comparative analysis of the measured EA cross-section, the calculated 5s2 ionization cross-section and the available ionization data showed that (i) direct ionization of the 5s2 shell and EA of the 4p6 shell adequately describe the single ionization of Sr atoms; (ii) 4p6 EA contribution reaches 25% of the total single ionization cross-section of Sr atoms.