Femtosecond photoelectron diffraction: A new approach to image molecular structure during photochemical reactions.

Continuing technical advances in the creation of (sub-) femtosecond VUV and X-ray pulses with Free-Electron Lasers and laser-based high-harmonic-generation sources have created new opportunities for studying ultrafast dynamics during chemical reactions. Here, we present an approach to image the geometric structure of gas-phase molecules with fewfemtosecond temporal and sub-Ångström spatial resolution using femtosecond photoelectron diffraction. This technique allows imaging the molecules “from within” by analyzing the diffraction of inner-shell photoelectrons that are created by femtosecond VUV and X-ray pulses. Using pump-probe schemes, ultrafast structural changes during photochemical reactions can thus be directly visualized with a temporal resolution that is only limited by the pulse durations of the pump and the probe pulse and the synchronization of the two light pulses. Here, we illustrate the principle of photoelectron diffraction using a simple, geometric scattering model and present results from photoelectron diffraction experiments on laser-aligned molecules using X-ray pulses from a Free-Electron Laser

Diffraction effects in the Recoil-Frame Photoelectron Angular Distributions of Halomethanes

Citation: Bomme, C., Anielski, D., Savelyev, E., Boll, R., Erk, B., Bari, S., . . . Rolles, D. (2015). Diffraction effects in the Recoil-Frame Photoelectron Angular Distributions of Halomethanes. 635(11). doi:10.1088/1742-6596/635/11/112020We have measured the Recoil Frame-Photoelectron Angular Distributions (RF-PADs) for inner-shell photoionization of CH3F, CH3I and CF3I halomethane molecules for photoelectron energies up to 300 eV detected within a 4? solid angle in the gas-phase. For high kinetic energies, the RF-PADs are dominated by diffraction effects that encode information on the molecular geometry. © Published under licence by IOP Publishing Ltd

Time-Resolved Measurement of Interatomic Coulombic Decay in Ne_2

The lifetime of interatomic Coulombic decay (ICD) [L. S. Cederbaum et al., Phys. Rev. Lett. 79, 4778 (1997)] in Ne_2 is determined via an extreme ultraviolet pump-probe experiment at the Free-Electron Laser in Hamburg. The pump pulse creates a 2s inner-shell vacancy in one of the two Ne atoms, whereupon the ionized dimer undergoes ICD resulting in a repulsive Ne^{+}(2p^{-1}) - Ne^{+}(2p^{-1}) state, which is probed with a second pulse, removing a further electron. The yield of coincident Ne^{+} - Ne^{2+} pairs is recorded as a function of the pump-probe delay, allowing us to deduce the ICD lifetime of the Ne_{2}^{+}(2s^{-1}) state to be (150 +/- 50) fs in agreement with quantum calculations.Comment: 5 pages, 3 figures, accepted by PRL on July 11th, 201

Coupled motion of Xe clusters and quantum vortices in He nanodroplets

Citation: Jones, C. F., Bernando, C., Tanyag, R. M. P., Bacellar, C., Ferguson, K. R., Gomez, L. F., . . . Vilesov, A. F. (2016). Coupled motion of Xe clusters and quantum vortices in He nanodroplets. Physical Review B - Condensed Matter and Materials Physics, 93(18). doi:10.1103/PhysRevB.93.180510Additional Authors: Erk, B.;Foucar, L.;Hartmann, R.;Neumark, D. M.;Epp, S. W.;Englert, L.;Siefermann, K. R.;Weise, F.;Rudek, B.;Sturm, F. P.;Ullrich, J.;Bostedt, C.;Gessner, O.;Vilesov, A. F.Single He nanodroplets doped with Xe atoms are studied via ultrafast coherent x-ray diffraction imaging. The diffraction images show that rotating He nanodroplets about 200 nm in diameter contain a small number of symmetrically arranged quantum vortices decorated with Xe clusters. Unexpected large distances of the vortices from the droplet center (?0.7-0.8 droplet radii) are explained by a significant contribution of the Xe dopants to the total angular momentum of the droplets and a stabilization of widely spaced vortex configurations by the trapped Xe clusters. © 2016 American Physical Society

Communication: X-ray coherent diffractive imaging by immersion in nanodroplets

Citation: Tanyag, R. M. P., Bernando, C., Jones, C. F., Bacellar, C., Ferguson, K. R., Anielski, D., . . . Vilesov, A. F. (2015). Communication: X-ray coherent diffractive imaging by immersion in nanodroplets. Structural Dynamics, 2(5), 9. doi:10.1063/1.4933297Lensless x-ray microscopy requires the recovery of the phase of the radiation scattered from a specimen. Here, we demonstrate a de novo phase retrieval technique by encapsulating an object in a superfluid helium nanodroplet, which provides both a physical support and an approximate scattering phase for the iterative image reconstruction. The technique is robust, fast-converging, and yields the complex density of the immersed object. Images of xenon clusters embedded in superfluid helium droplets reveal transient configurations of quantum vortices in this fragile system. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.Additional Authors: Neumark, D. M.;Rolles, D.;Rudek, B.;Rudenko, A.;Siefermann, K. R.;Ullrich, J.;Weise, F.;Bostedt, C.;Gessner, O.;Vilesov, A. F

Imaging Molecular Structure through Femtosecond Photoelectron Diffraction on Aligned and Oriented Gas-Phase Molecules

This paper gives an account of our progress towards performing femtosecond time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe setup combining optical lasers and an X-ray Free-Electron Laser. We present results of two experiments aimed at measuring photoelectron angular distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C8H5F) and dissociating, laseraligned 1,4-dibromobenzene (C6H4Br2) molecules and discuss them in the larger context of photoelectron diffraction on gas-phase molecules. We also show how the strong nanosecond laser pulse used for adiabatically laser-aligning the molecules influences the measured electron and ion spectra and angular distributions, and discuss how this may affect the outcome of future time-resolved photoelectron diffraction experiments.Comment: 24 pages, 10 figures, Faraday Discussions 17

towards time-resolved imaging of molecular structure

We demonstrate an experimental method to record snapshot diffraction images of polyatomic gas-phase molecules, which can, in a next step, be used to probe time-dependent changes in the molecular geometry during photochemical reactions with femtosecond temporal and angstrom spatial resolution. Adiabatically laser-aligned 1-ethynyl-4-fluorobenzene (C8H5F) molecules were imaged by diffraction of photoelectrons with kinetic energies between 31 and 62 eV, created from core ionization of the fluorine (1s) level by ≈80 fs x-ray free-electron-laser pulses. Comparison of the experimental photoelectron angular distributions with density functional theory calculations allows relating the diffraction images to the molecular structure

Charge separation relative to the reaction plane in Pb-Pb collisions at sNN=2.76\sqrt{s_{\rm NN}}= 2.76 TeV

Measurements of charge dependent azimuthal correlations with the ALICE detector at the LHC are reported for Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV. Two- and three-particle charge-dependent azimuthal correlations in the pseudo-rapidity range $|\eta| < 0.8$ are presented as a function of the collision centrality, particle separation in pseudo-rapidity, and transverse momentum. A clear signal compatible with a charge-dependent separation relative to the reaction plane is observed, which shows little or no collision energy dependence when compared to measurements at RHIC energies. This provides a new insight for understanding the nature of the charge dependent azimuthal correlations observed at RHIC and LHC energies.Comment: 12 pages, 3 captioned figures, authors from page 2 to 6, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/286

A note on comonotonicity and positivity of the control components of decoupled quadratic FBSDE

In this small note we are concerned with the solution of Forward-Backward Stochastic Differential Equations (FBSDE) with drivers that grow quadratically in the control component (quadratic growth FBSDE or qgFBSDE). The main theorem is a comparison result that allows comparing componentwise the signs of the control processes of two different qgFBSDE. As a byproduct one obtains conditions that allow establishing the positivity of the control process.Comment: accepted for publicatio