title: Double-core-hole spectroscopy for chemical analysis with an intense X-ray femtosecond laser.
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.
authors.affiliation: Physics Department, Western Michigan University, Kalamazoo, MI 49008, USA. nora.berrah@wmich.edu
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authors.lastname: Berrah
authors.forename: Li
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authors.lastname: Murphy
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authors.lastname: Larsson
authors.forename: Robert
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authors.lastname: Richter
authors.forename: Kevin C
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authors.lastname: Bozek
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authors.lastname: Wada
authors.forename: Maria N
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authors.lastname: Piancastelli
authors.forename: Motomichi
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authors.lastname: Tashiro
authors.forename: Masahiro
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authors.lastname: Ehara