The 5p autoionization spectra of Ba atoms excited by electron impact: identification of lines

The ejected-electron spectra corresponding to the radiationless decay of 5p(5)n(1)l(1)n(2)l(2)n(3)l(3) states in Ba atoms have been measured precisely for different incident electron energies ranging from the appearance of the first autoionizing line at 15.68 eV up to 140 eV. The spectra have been obtained at an observation angle of 54.7 degrees and with incident-electron and ejected-electron energy resolutions of 0.2 eV and 0.07 eV, respectively. In total, 63 lines with excitation thresholds below 22 eV have been observed between 9.8 and 16.6 eV ejected-electron kinetic energy. Based on measured excitation energies, intensity behavior of lines, calculated excitation energies, cross sections and decay rates of states in 5p(5)6s(2)nl, 5p(5)5d(2)nl and 5p(5)5d6snl configurations, assignments for all 63 lines are proposed. The excitation and decay processes for classified autoionizing states have been examined and compared with existing data. The excitation threshold of the 5p(6) subshell has been established at 15.61 +/- 0.05 eV.