The 5p6 autoionization cross section of cesium atoms: contribution to single ionization by electron impact

Abstract

The autoionization cross section of cesium atoms in the incident electron energy range from the 5p6 lowest autoionization threshold at 12.3 eV up to 16.6 eV was investigated for the first time. The data were obtained by summarizing the normalized intensities of lines in ejected-electron spectra observed at the ‘magic’ angle of 54.7°. The autoionization cross section possesses a clear resonance character with a maximum value of 4.8 × 10−16 cm2 at 14.7 eV. By analysing the calculated multiconfiguration Dirac–Fock energies, decay channels and excitation cross sections for the lowest autoionizing configurations it was found that the quartet levels 5p55d6s give the bulk of the autoionization cross section and, therefore, of the autoionization contribution to the single ionization cross section of cesium. Both resonance shape and ‘fine’ structure of the autoionization cross section are caused by the presence of strong negative-ion resonances in the excitation of the levels in configurations 5p56s2, 5p55d6s and 5p56s6p. A comparison of the data is made with available experimental and theoretical electron impact single ionization cross sections of cesium atoms.