Inner-shell photodetachment fromRu−

Abstract

Inner-shell photodetachment from Ru − was studied near and above the 4p excitation region, 29-to-91-eV photon energy range, using a merged ion-photon-beam technique. The absolute photodetachment cross sections of Ru − ([Kr] 4d 7 5s 2 ) leading to Ru + , Ru 2+ , and Ru 3+ ion production were measured. In the near-threshold region, a Wigner s-wave law, including estimated postcollision interaction effects, locates the 4p 3/2 detachment threshold between 40.10 and 40.27 eV. Additionally, the Ru 2+ product spectrum provides evidence for simultaneous two-electron photodetachment (likely to the Ru + 4p 5 4d 6 5s 2 state) located near 49 eV. Resonance effects are observed due to interference between transitions of the 4p electrons to the quasibound 4p 5 4d 8 5s 2 states and the 4d → εf continuum. Despite the large number of possible terms resulting from the Ru − 4d open shell, the cross section obtained from a 51-state LS-coupled R-matrix calculation agrees qualitatively well with the experimental data.

Inner-shell photodetachment from Ni− : A giant Feshbach resonance

“…For the photoionization of the Ni atoms, ratio of Ni 2+ /Ni + slowly rises from a value of 0.15 ± 0.03 at 68 eV to 0.58 ± 0.04 at 80 eV [36]. Similar behavior was observed for photoionization of Co, and Fe atoms [36] and for photodetachment of Fe¯ [23]. A broad feature is observed near 70 eV in the Ni + channel and is not readily seen in the other channels.…”

“…Since they are often located very close to a threshold, the corresponding Wigner threshold behavior is severely altered by their presence as pointed out by Peterson et al [11,12]. Such shape resonances have been reported in other inner-shell photodetachment studies such as in Li ¯ [13,14,15,16], B¯ [17,18,19], C¯ [20,21,22], Fe¯ [23] and Ru¯ [24]. Both types of resonances were observed in the Pt¯ ion [25].…”

“…Figure 3 shows the absolute photodetachment cross section of Ni¯ to the Ni + , Ni 2+ , and Ni 3+ product channels. The circles with error bars in Figure 3 represent the absolute cross section measurements to which the spectra are normalized by using the same method as in previous experiments [9,23,24,52]. Production of Ni 3+ is possible only above the 4-electron threshold at 62.153 (19) [47], and most likely involves highly correlated many-electron processes over the photon energy range scanned in this experiment, 60 -90 eV.…”

“…In order to gain a qualitative understanding of the resonance phenomena occurring in the complete Ni¯ inner-shell photodetachment process, we performed lowerorder calculations using the R-matrix method [54,55]. In this study, we follow the basic theoretical methodology used for R-matrix calculations for Li¯ [13], B¯ [17,18], C¯ [20,21], Fe¯ [23], and Ru¯ [24], and seek a minimal configuration and orbital basis for capturing the essential physics. For the present Ni¯ photodetachment case, we first included all symmetries consistent with the photodetachment process at hand: Ni¯(3p 6 3d 9 4s 2 ) → Ni(3p 6 3d 8 4s 2 ).…”

Threshold behavior of positronium formation in positron–alkali-metal scattering

“…The derived threshold laws were found to be applicable for the description of a rich variety of collision processes [2]. Initially, studies of threshold effects utilized collisions involving electrons [3] and positrons [4][5][6][7]. Their longer wavelengths allowed characterization of the scattering process using few parameters over a substantial energy range.…”