Experimental study of 4f wavefunction contraction: 4d-photoionization of low-charged ions of I, Xe, Cs and Ba

Abstract

The photon-ion merged beam technique has been used to measure the ionization cross sections of I-, Cs+, Ba+ and Ba2+ ions in the energy region from 40 to 185 eV, which is dominated by photoexcitation from the 4d shell (the experimental data are available at http://www.ifa.au.dk/amo/atomphys/atomphys.htm). Within the experimental accuracy, the total oscillator strengths for these ions and for the I+, I2+, Xe+ and Xe2+ ions, that were recently studied by some of the present authors, are identical, with the contribution from the 4d → np or nf resonances becoming more important with increasing nuclear charge and ionization stage, and with the maximum value of the continuum cross section increasing as the nuclear number is enlarged. The present data support the assumption that the 4f wavefunctions contract gradually with increasing ionization, both along isonuclear and isoelectronic sequences, for ionic charges ranging from -1 to +2.

Solvent Dependence of the Electronic Structure of I– and I3–

“…As far as we know, there are no published data on the 4d binding energies of gas-phase I – . The I – photoionization cross section has been measured in a merged beam experiment . Unfortunately, the lack of sharp resonances in the I – 4d excitation spectrum makes it difficult to exactly determine the ionization potential of the 4d levels, but the onset of increased photoionization cross section lies close to 50 eV, in good agreement with our calculated value.…”

“…The I − photoionization cross section has been measured in a merged beam experiment. 49 Unfortunately, the lack of sharp resonances in the I − 4d excitation spectrum makes it difficult to exactly determine the ionization potential of the 4d levels, but the onset of increased photoionization cross section lies close to 50 eV, in good agreement with our calculated value. Assuming the same binding energy difference between I3d and I4d in the gas and solution phase, a value of 49.3 eV can be estimated from experimental gas-phase data and is close to our calculated value.…”

Photoionisation cross sections of atomic ions

“…This leads to further improvements in theoretical methods and also to a critical examination of experimental data where there is marked disagreement with theory. In this field theory and experiment are now proceeding hand-in-hand; as has been seen earlier in this article, the experimental data are not always reliable, Kjeldsen et al (2002). Lower part: Ba þ data from Koizumi et al (1995).…”

“…In Fig. 14 are shown the absolute measurements obtained at the ASTRID storage ring for I À ; Cs þ and Ba 2þ (Kjeldsen et al, 2002), together with earlier measurements on neutral Xe (West and Morton, 1978). From these data it can be ascertained that the oscillator strength contained in the 4d peak reduces only slightly as one proceeds along the sequence from I À to Ba 2þ : If the cross section is partitioned into single, double and triple ionisation, then it can be seen that the discrete structure dominates the single ionisation channel; this is because the single ionisation yield comes either from direct ionisation of the outer shell electrons, or from discrete levels of the singly charged ion which then autoionise into the doubly charged ion continuum with ejection of an outer shell electron.…”

The barium giant dipole resonance in barite: a study of soft X-ray absorption edges using hard X-rays

“…This is supported by comparing the shape of the giant resonance observed by NRIXS with the experimental total photoionization cross sections reported for single-ionized barium. 78 The experimental spectrum obtained for the smallest momentum transfer is compared with calculations of the giant resonance in the dipole limit as presented in Fig. 2.…”