Title: Observing pre-edge $K$-shell resonances in Kr, Xe, and ${\mathrm{XeF}}_2$

Abstract

The 1s→np Rydberg transitions below the 1s ionization thresholds of Kr and Xe are obscured in x-ray absorption spectra due to core-hole lifetime broadening. However, the np spectator electrons associated with those resonances can affect the core-hole decay spectra. We report on ion charge-state distributions of Kr and Xe measured in coincidence with KL _2,3 (K _α1,2), KM _2,3 (Kβ _1,3), and KN _2,3 (Kβ ₂) x-ray fluorescence as the incident x-ray energy is scanned through pre-edge resonances and ionization thresholds. The coincidence measurements select vacancy cascades that begin with a radiative transition that transfers 1s holes to the 2p, 3p, and 4p shells followed by emission of Auger electrons. We observe shifts of ion yields from higher to lower charge states that we attribute to np spectator electrons. For the special case of Kr ¹⁺ that is produced in coincidence with Kβ ₂ x rays, the ion yield decreases in the pre-edge region. This is attributed to production of neutral, metastable Kr 4p ^–1np states that reduce the Kr ¹⁺ yield. Model fits to the x-ray absorption spectra are presented to show the lifetime broadened pre-edge resonances and ionization thresholds. High-level relativistic coupled-cluster calculations that treat relativistic, electron correlation,more » and wave function relaxation effects on the same footing obtain agreement with the experimental 1s ionization energies of Kr and Xe to <2 eV. The Xe K-edge x-ray absorption spectrum and ion charge-state distributions of XeF2 were also recorded. Excitation of the 7σ _u lowest unoccupied molecular orbital (LUMO) in XeF ₂ is observed in the pre-edge region. Our ab initio calculations find that the 6p _z Rydberg state is strongly perturbed by the presence of the 7σu LUMO. A fit to the measured LUMO, 6p _x, 6p _y, 6p _z Rydberg states, and ionization threshold is guided by the relativistic coupled-cluster calculations. The F ligands modify the valence electron charge distribution and result in a ~2.3 eV chemical shift of the Xe 1s ionization energy relative to atomic Xe. Xe 1s ^–1 core-hole decay in XeF ₂ results in ionization of the F ligands and energetic fragmentation into atomic ions. Ion charge-state spectra of XeF ₂ were recorded in coincidence with x-ray fluorescence for excitation on the LUMO resonance and above the Xe 1s ionization threshold. For the ion time of flight spectra recorded on the LUMO resonance, the F ^q+ (q = 1–4) peaks are split into two peaks along the linear polarization direction of the incident x-ray beam. This effect is attributed to spatial alignment of XeF ₂ molecules by resonant x-ray absorption, and the peak splittings are used to measure the F ion fragmentation energies following Kα _1,2, Kβ _1,3, and Kβ ₂ x-ray fluorescence. Here, we observe variations of the F ion charge state yields and fragmentation energies for the three fluorescence pathways that leave the molecule in different outer-shell hole states.« less

Authors:

Southworth, S. H. ^[1]; Dunford, R. W. ^[1]; Ray, D. ^[2]; Kanter, E. P. ^[1]; Doumy, G. ^[1]; March, A. M. ^[1]; Ho, P. J. ^[1]; Krässig, B. ^[1]; Gao, Y. ^[3]; Lehmann, C. S. ^[4]; Picón, A. ^[5]; Young, L. ^[6]; Walko, D. A. ^[1]; Cheng, L. ^[7]

---

+ Show Author Affiliations

1. Argonne National Lab. (ANL), Lemont, IL (United States)
2. Argonne National Lab. (ANL), Lemont, IL (United States); KLA Corp., Milpitas, CA (United States)
3. Argonne National Lab. (ANL), Lemont, IL (United States); Brookhaven National Lab. (BNL), Upton, NY (United States)
4. Argonne National Lab. (ANL), Lemont, IL (United States); Philipps-Univ. Marburg, Marburg (Germany)
5. Argonne National Lab. (ANL), Lemont, IL (United States); Univ. Autónoma de Madrid, Madrid (Spain)
6. Argonne National Lab. (ANL), Lemont, IL (United States); The Univ. of Chicago, Chicago, IL (United States)
7. Johns Hopkins Univ., Baltimore, MD (United States)

Publication Date:

2019-08-09

Research Org.:

Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; USDOE

OSTI Identifier:

1559935

Alternate Identifier(s):

OSTI ID: 1550585

Grant/Contract Number:  

AC02-06CH11357

Resource Type:

Journal Article: Accepted Manuscript

Journal Name:

Physical Review A

Additional Journal Information:

Journal Volume: 100; Journal Issue: 2; Journal ID: ISSN 2469-9926

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

74 ATOMIC AND MOLECULAR PHYSICS