A study of 5p excitation in atomic barium. I. The 5p absorption spectra of Ba 1, Cs 1 and related elements

Abstract

New observations of the 5p spectra of Cs i and Ba i are reported. The extreme complexity of the structure does not permit precise configuration labels to be attached to all the excited levels. Nevertheless, more than 160 transitions in Ba i have been ordered into 14 series converging on experimentally known levels of the parent ion. An attempt has been made to analyse the limit structure by comparison with the data for Cs I and Hartree-Fock atomic structure calculations. The results obtained are consistent with previous interpretations of the double ionization anomaly in Ba I. Further comments are made on the comparison between experiment and the predictions of the r.p.a.e. theory for 5p excitation in Ba i. It is shown that the 5p 6 6s 2 S 1/2 -> 5p 5 6s 2 2 P 1/2 and 2 P 3/2 transitions of Cs i have been incorrectly identified and new assignments are proposed.

Study of Characteristics of AC Arc Discharges on Polluted Insulator Surfaces

“…To control the stability of the experimental conditions, a 'test' spectrum at the impact energy of 12.5 eV was measured before and after each set of five ejected-electron spectra. The ejected-electron energy scale was calibrated by using photoabsorption data [16] for the (5p 5 6s 2 ) 2 P 3/2 state at 12.305 eV. The incident-electron energy scale was calibrated by comparing the relative position of the 5p 6 6p, 5d and 7s energy-loss lines [17] and the (5p 5 6s 2 ) 2 P 3/2 ejected-electron line at 8.41 eV in spectra measured at impact energy values of 14 eV.…”

“…In addition to the 63 lines observed earlier in high-resolution spectra [19], new lines X1 and X2 at 16.18 eV and 17.36 eV, respectively, were observed in the present spectra at impact energies below 30 eV (see table 1). Using the photoabsorption data [16], some of the low-energy lines were assigned as belonging to autoionizing states with configurations 5p 5 6s 2 and 5p 5 5d6s. Note, however, that due to a strong configuration mixing effect [16], the LS-coupling scheme is not a good approximation for assigning even the low-lying core-excited configurations in caesium.…”

“…Using the photoabsorption data [16], some of the low-energy lines were assigned as belonging to autoionizing states with configurations 5p 5 6s 2 and 5p 5 5d6s. Note, however, that due to a strong configuration mixing effect [16], the LS-coupling scheme is not a good approximation for assigning even the low-lying core-excited configurations in caesium. Lacking accurate theoretical calculations, the remaining lines were conditionally classified as (dipole) allowed or (dipole) forbidden autoionizing states depending, respectively, on their presence or absence in the photoabsorption spectra [16].…”

“…Note, however, that due to a strong configuration mixing effect [16], the LS-coupling scheme is not a good approximation for assigning even the low-lying core-excited configurations in caesium. Lacking accurate theoretical calculations, the remaining lines were conditionally classified as (dipole) allowed or (dipole) forbidden autoionizing states depending, respectively, on their presence or absence in the photoabsorption spectra [16]. The above data show an interesting feature of the energy level structure in caesium atoms.…”

Electron impact on laser excited barium atoms

“…Wolfgang Hink died in December 1991, few days before his 68th birthday, and few months before his retirement from the University of Wfirzburg Due to its high atomic number (Z = 56) the model of LS coupling begins to fail, especially in neutral and singly ionized barium. This is the explanation of the unexpected complexity of photoabsorption spectra [4], or Auger decay following electron impact [5,6]. Multiconfiguration Dirac-Fock calculations of neutral [7] and singly ionized [8] barium were able to explain many of the experimental data, but, due to the limited set of available observables, left many questions about the details of the wave functions unanswered.…”