Electron-Impact Excitation of the 5p55d6s2 Autoionizing States in Ba Atom

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.

Особенности возбуждения линий главной серии атомов подгруппы цинка электронным ударом. II. Цинк

Using the technique of crossed beams of slow electrons and zinc atoms, the excitation functions of four spectral lines of Zn I principal series corresponding to the 4snp 1Po1  4s2 1S0 transitions for n = 4, 5, 6, 7 are measured. Their wavelengths are 213.9, 158.9, 145.8, 140.4 nm, respectively. In the energy range 11–18 eV, these functions revealed the manifestation of the effect of collision interaction of electrons (slow scattered and fast emitted) during the decay of the autoionization state. At incident electron energies of 11–13 and 15–18 eV, this interaction leads to an additional population of the initial levels for these lines and, correspondingly, to the formation of maxima on their excitation functions due to the capture of the scattered electron at the indicated excited levels. The terms of autoionizing states of the atom responsible for the observed maxima are established. The combined effect of the decay of these autoionizing states and the post-collision interaction is expressed in the energy shift of the maxima on the excitation functions relative to the positions of the corresponding autoionizing states. In the classical approximation, the effective widths of the electronic decay of autoionizing states are estimated by direct calculations. For the estimations, exact and approximate formulas are used. The latter are valid for various relations between the magnitude of the post-collision shift of the maxima on the excitation functions and the electron binding energy at the atomic level. They are used to determine the effective widths when the experimental shifts are approximated by the least squares method.