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Time-resolved x-ray absorption spectroscopy with a water window high-harmonic source

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Science  20 Jan 2017:
Vol. 355, Issue 6322, pp. 264-267
DOI: 10.1126/science.aah6114

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An x-ray view of C–F and S–F bond breaks

X-ray absorption spectroscopy is a useful probe of element-specific dynamics in molecular reactions. However, the required x-ray fluxes have rarely been available outside expensive dedicated facilities such as synchrotrons. Pertot et al. developed a tabletop laser-based high-harmonic source that extends far enough into the x-ray region to probe carbon K-edge and sulfur L-edge absorptions with femtosecond temporal resolution. They used this source to track the previously elusive dissociative dynamics of gaseous carbon tetrafluoride and sulfur hexafluoride after laser-induced ionization.

Science, this issue p. 264

Abstract

Time-resolved x-ray absorption spectroscopy (TR-XAS) has so far practically been limited to large-scale facilities, to subpicosecond temporal resolution, and to the condensed phase. We report the realization of TR-XAS with a temporal resolution in the low femtosecond range by developing a tabletop high-harmonic source reaching up to 350 electron volts, thus partially covering the spectral region of 280 to 530 electron volts, where water is transmissive. We used this source to follow previously unexamined light-induced chemical reactions in the lowest electronic states of isolated CF4+ and SF6+ molecules in the gas phase. By probing element-specific core-to-valence transitions at the carbon K-edge or the sulfur L-edges, we characterized their reaction paths and observed the effect of symmetry breaking through the splitting of absorption bands and Rydberg-valence mixing induced by the geometry changes.

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