ELECTRON-IMPACT EXCITATION OF THE 5p55d6s2 AUTOIONIZING STATES IN Ba ATOM

Abstract

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 incidentelectron 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.