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Attosecond Delays in X-ray Molecular Ionization

Published on by Taran Driver

The photoelectric effect is not truly instantaneous, but exhibits attosecond delays that can reveal complex molecular dynamics. Sub-femtosecond duration light pulses provide the requisite tools to resolve the dynamics of photoionization. Accordingly, the past decade has produced a large volume of work on photoionization delays following single photon absorption of an extreme ultraviolet (XUV) photon. However, the measurement of time-resolved core-level photoionization remained out of reach. 

The required x-ray photon energies needed for core-level photoionization were not available with attosecond tabletop sources. We have now measured the x-ray photoemission delay of core-level electrons, and here report unexpectedly large delays, ranging up to 700 attoseconds in NO near the oxygen K-shell threshold. These measurements exploit attosecond soft x-ray pulses from a free-electron laser (XFEL) to scan across the entire region near the K-shell threshold. Furthermore, we find the delay spectrum is richly modulated, suggesting several contributions including transient trapping of the photoelectron due to shape resonances, collisions with the Auger-Meitner electron that is emitted in the rapid non-radiative relaxation of the molecule, and multi-electron scattering effects. The results demonstrate how x-ray attosecond experiments, supported by comprehensive theoretical modelling, can unravel the complex correlated dynamics of core-level photoionization.

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Funding

This work was supported primarily by the AMO Physics Program, Chemical Sciences, Geosciences and Biosciences Division (CSGB), BES, DOE

Use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES) under Contract No. DE-AC02-76SF00515

A.M. J.D., and Z.G. acknowledge support from the Accelerator and Detector Research Program of the Department of Energy, Basic Energy Sciences division.

A.L. and L.O. were supported by DOE Investigator-Initiated Research grant, Award ID DE-SC0022093, of CSGB, BES, DOE.

N.B. acknowledges support from Chemical Sciences, Geosciences and Biosciences Division (CSGB), BES, DOE under award No DE-SC0012376

P.R. and M.F.K. acknowledge support by the German Research Foundation through LMUexcellent

I.I. acknowledges support from the Institute for Basic Science grant (IBS-R012-D1)

R.R.L. acknowledges support from CSGB, BES, DOE under contract no. DE-AC02-05CH11231

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