Double-core-hole spectroscopy for chemical analysis with an intense X-ray femtosecond laser - PubMed (original) (raw)

. 2011 Oct 11;108(41):16912-5.

doi: 10.1073/pnas.1111380108. Epub 2011 Oct 3.

Li Fang, Brendan Murphy, Timur Osipov, Kiyoshi Ueda, Edwin Kukk, Raimund Feifel, Peter van der Meulen, Peter Salen, Henning T Schmidt, Richard D Thomas, Mats Larsson, Robert Richter, Kevin C Prince, John D Bozek, Christoph Bostedt, Shin-ichi Wada, Maria N Piancastelli, Motomichi Tashiro, Masahiro Ehara

Affiliations

Double-core-hole spectroscopy for chemical analysis with an intense X-ray femtosecond laser

Nora Berrah et al. Proc Natl Acad Sci U S A. 2011.

Abstract

Theory predicts that double-core-hole (DCH) spectroscopy can provide a new powerful means of differentiating between similar chemical systems with a sensitivity not hitherto possible. Although DCH ionization on a single site in molecules was recently measured with double- and single-photon absorption, double-core holes with single vacancies on two different sites, allowing unambiguous chemical analysis, have remained elusive. Here we report that direct observation of double-core holes with single vacancies on two different sites produced via sequential two-photon absorption, using short, intense X-ray pulses from the Linac Coherent Light Source free-electron laser and compare it with theoretical modeling. The observation of DCH states, which exhibit a unique signature, and agreement with theory proves the feasibility of the method. Our findings exploit the ultrashort pulse duration of the free-electron laser to eject two core electrons on a time scale comparable to that of Auger decay and demonstrate possible future X-ray control of physical inner-shell processes.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

Schematic illustration of (A) the electronic structure of the CO molecule, (B) the SCH ionization at the C K-edge (SCH_C) and the SCH ionization at the O K-edge (SCH_O), and (C) the ssDCH ionization at the C K-edge (ssDCH_C), the ssDCH ionization of the O K-edge (ssDCH_O) and the tsDCH ionization.

Fig. 2.

Fig. 2.

Photoelectron spectra of carbon recorded at 700 eV photon energy, approximately 10 fs pulse duration. Calculated state energies and intensities are marked by vertical thick lines with head markers: tsDCH (dashed line), ssDCH (solid line), and SCH of CO+ with a valence hole (dash-dotted). The calculated energies for atomic ions are marked by a group of solid vertical lines without head markers. The spectra are calibrated to the known experimental binding energy value of the CO SCH that is marked by the thin dashed line (see text and Materials and Methods for details).

Fig. 3.

Fig. 3.

Photoelectron spectra demonstrating consistent structures measured with two experimental methods. (A, Upper) Photoelectron spectrum resulting from the subtraction of spectra measured above and below the O-K-edge. (B, Lower) Represents Fig. 2 (red filled part) and is compared to the Upper panel to demonstrate the observation of tsDCH in the photoelectron spectrum.

Fig. 4.

Fig. 4.

Auger spectra compared to theoretical DCH Auger spectra. Measurements taken at different X-ray intensities with a focused beam (red curve in Inset) and a defocused beam (blue curve in Inset). The purple curve was taken with synchrotron radiation and is shown for comparison. The difference of the two X-ray intensities is shown as the black curve. Theoretical Auger spectra are shown in the main panel: overall calculation (yellow shaded area); ssDCH (solid blue curve); tsDCH (solid red curve); ssDCH secondary processes (dashed blue curve); tsDCH secondary processes (dashed red curve).

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