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.multi-photon ionization | ultrafast | two-photon spectroscopy

Double core-hole formation in small molecules at the LCLS free electron laser

“…Our experimentally determined values of IRC follow the trends, and support, this theory. Further, the chemical sensitivity of the tsDCH was exemplified by the large spectral shift of the O -1 C -1 tsDCH state of CO 2 with respect to that of CO [18], which is induced by the extra O atom.…”

“…Hence, by determining ΔE 2 from the spectra of the molecules N 2 , N 2 O, CO 2 and CO [18], we may test the predicted sensitivity of the tsDCH state to the chemical environment in the following way. By comparing N 2 and N 2 O with respect to ΔE 2 of the N -1 N -1 tsDCH state, and comparing CO and CO 2 with respect to ΔE 2 of the O -1 C -1 tsDCH state, the influence of the additional O atom on ΔE 2 may be investigated in both cases.…”

“…In the first experiments at the atomic, molecular and optical science (AMO) instrument with N 2 as target molecule for the LCLS beam, single-site double core vacancies were observed [16,17]. In the next generation of experiments, two-site double corehole states were observed in a molecule (CO) for the first time [18], and used to explore the chemical sensitivity of these states in CO 2 , N 2 O and N 2 [19]. The realization of the LCLS has inspired theoretical work [21][22][23] along the lines initiated by Cederbaum and co-workers 25 years ago [7,8].…”

Nonthermal graphitization of diamond induced by a femtosecond x-ray laser pulse

“…The fourth-generation light sources, the free-electron lasers (FEL), such as FLASH, 1 LCLS, 2 SACLA, 3 and FERMI, 4 stimulate rapid advances in many scientific fields, including investigation of atoms, 5,6 molecules, 7,8 clusters, 9,10 and solids [11][12][13] exposed to intense laser fields. It enables creating and probing plasmas, 14,15 hot dense matter, [15][16][17] and warm dense matter, 18,19 as well as the investigation of the interaction of low-fluence ultrafast laser pulses with matter, with applications to structural studies within solidstate physics, 11,[20][21][22][23] nanophysics, 24 molecular physics, and biophysics.…”

Homonuclear site-specific photochemistry by an ion–electron multi-coincidence spectroscopy technique

“…Refs. [27][28][29][30]) because of the coulomb repulsion. Secondly, the electrons taking part in the Auger effect come from orbitals with greatest density at the core-hole site; generally the bond weakening upon their loss will also be located in the same vicinity.…”