Dynamics of Hollow Atom Formation in Intense X-Ray Pulses Probed by Partial Covariance Mapping

Abstract

When exposed to ultraintense x-radiation sources such as free electron lasers (FELs) the innermost electronic shell can efficiently be emptied, creating a transient hollow atom or molecule. Understanding the femtosecond dynamics of such systems is fundamental to achieving atomic resolution in flash diffraction imaging of noncrystallized complex biological samples. We demonstrate the capacity of a correlation method called "partial covariance mapping" to probe the electron dynamics of neon atoms exposed to intense 8 fs pulses of 1062 eV photons. A complete picture of ionization processes competing in hollow atom formation and decay is visualized with unprecedented ease and the map reveals hitherto unobserved nonlinear sequences of photoionization and Auger events. The technique is particularly well suited to the high counting rate inherent in FEL experiments.

Femtosecond X-ray-induced explosion of C60 at extreme intensity

“…A collimated molecular beam of C 60 molecules from a resistively heated oven crossed the X-ray path at the focus. A magnetic bottle spectrometer, previously used at the LCLS for electron correlation studies 31 , was outfitted with electrostatic lenses, which allowed KEresolved ion time-of-flight (TOF) spectroscopy with high collection efficiency, even at several hundred eV ion KE. A 2-m-long ion drift path provided high ion massto-charge and KE resolution while avoiding overlap of different fragment ion ) show agreement between the two models (purple for full model and green for full model without bonds) in the short pulse, high-fluence case (in this example, photon energy is 485 eV, pulse duration 4 fs and fluence 550 J cm À 2 ).…”

“…Specifically, we demonstrate the effects of high per-atom X-ray absorption on the fragmentation dynamics of C 60 molecules in the gas phase. C 60 offers a number of advantages as a benchmark molecule when compared with isolated atoms [29][30][31][32][33] , small molecules [34][35][36][37][38][39][40] or van der Waals (vdW) clusters 41,42 , from the perspective of radiation damage. C 60 consists of chemically bonded carbon atoms with representative bond lengths and damage processes.…”

Molecular Dynamics of XFEL-Induced Photo-Dissociation, Revealed by Ion-Ion Coincidence Measurements

“…Various experimental set-ups, as well as analysis methods, have been developed towards this goal. Most usable at FEL sources so far have been electron and ion time-of-flight (TOF) spectrometers and their various developments, such as COLTRIMS for ion-electron coincidences [16,17], and magnetic bottle spectrometers for electrons [18][19][20][21][22][23].…”

Multiple ionization and fragmentation dynamics of molecular iodine studied in IR–XUV pump–probe experiments

“…This way so-called hollow atoms with multiple core holes are created, where the inner-shells are depleted. 20,21 In general this requires higher intensities, shorter pulses, or larger photon energies where longer, more complicated Auger cascades are initiated. Therefore, we assume that these effects are negligible for our FEL pulse parameters.…”