P. Selles

Bio: P. Selles is an academic researcher from University of Paris. The author has contributed to research in topics: Ionization & Spectroscopy. The author has an hindex of 11, co-authored 21 publications receiving 411 citations. Previous affiliations of P. Selles include Centre national de la recherche scientifique.

Properties of hollow molecules probed by single-photon double ionization.

Abstract: The formation of hollow molecules (with a completely empty K shell in one constituent atom) through single-photon core double ionization has been demonstrated using a sensitive magnetic bottle experimental technique combined with synchrotron radiation. Detailed properties are presented such as the spectroscopy, formation, and decay dynamics of the N(2)(2+) K(-2) main and satellite states and the strong chemical shifts of double K holes on an oxygen atom in CO, CO2, and O2 molecules.

Evidence of single-photon two-site core double ionization of C2H2 molecules.

Abstract: We observe the formation in a single-photon transition of two core holes, each at a different carbon atom of the C2H2 molecule. At a photon energy of 770.5 eV, the probability of this 2-site core double ionization amounts to 1.6 ± 0.4% of the 1-site core double ionization. A simple theoretical model based on the knockout mechanism gives reasonable agreement with experiment. Spectroscopy and Auger decays of the associated double core hole states are also investigated.

Double-Core-Hole States in Neon: Lifetime, Post-Collision Interaction, and Spectral Assignment.

Abstract: Using synchrotron radiation and high-resolution electron spectroscopy, we have directly observed and identified specific photoelectrons from K^{-2}V states in neon corresponding to simultaneous 1s ionization and 1s→valence excitation. The natural lifetime broadening of the K^{-2}V states and the relative intensities of different types of shakeup channels have been determined experimentally and compared to ab initio calculations. Moreover, the high-energy Auger spectrum resulting from the decay of Ne^{2+}K^{-2} and Ne^{+}K^{-2}V states as well as from participator Auger decay from Ne^{+}K^{-1}L^{-1}V states, has been measured and assigned in detail utilizing the characteristic differences in lifetime broadenings of these core hole states. Furthermore, post collision interaction broadening of Auger peaks is clearly observed only in the hypersatellite spectrum from K^{-2} states, due to the energy sharing between the two 1s photoelectrons which favors the emission of one slow and one fast electron.

Single Photon K − 2 and K − 1 K − 1 Double Core Ionization in C 2 H 2 n ( n = 1 – 3 ), CO, and N 2 as a Potential New Tool for Chemical Analysis

Abstract: We have observed single photon double $K$-shell photoionization in the ${\mathrm{C}}_{2}{\mathrm{H}}_{2n}$ ($n=1--3$) hydrocarbon sequence and in ${\mathrm{N}}_{2}$ and CO, using synchrotron radiation and electron coincidence spectroscopy. Our previous observations of the ${K}^{\ensuremath{-}2}$ process in these molecules are extended by the observations of a single photon double photoionization with one core hole created at each of the two neighboring atoms in the molecule (${K}^{\ensuremath{-}1}{K}^{\ensuremath{-}1}$ process). In the ${\mathrm{C}}_{2}{\mathrm{H}}_{2n}$ sequence, the spectroscopy of ${K}^{\ensuremath{-}1}{K}^{\ensuremath{-}1}$ states is much more sensitive to the bond length than conventional electron spectroscopy for chemical analysis spectroscopy based on single $K$-shell ionization. The cross section variation for single photon ${K}^{\ensuremath{-}1}{K}^{\ensuremath{-}1}$ double core ionization in the ${\mathrm{C}}_{2}{\mathrm{H}}_{2n}$ sequence and in the isoelectronic ${\mathrm{C}}_{2}{\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$ and CO molecules validates a knock-out mechanism in which a primary ionized $1s$ photoelectron ejects another $1s$ electron of the neighbor atom. The specific Auger decay from such states is clearly observed in the CO case.

Near-edge x-ray absorption fine structures revealed in core ionization photoelectron spectroscopy.

Abstract: Simultaneous core ionization and core excitation have been observed in the C(2)H(2n) (n=1, 2, 3) molecular series using synchrotron radiation and a magnetic bottle time-of-flight electron spectrometer. Rich satellite patterns corresponding to (K(-2)V) core excited states of the K(-1) molecular ions have been identified by detecting in coincidence the photoelectron with the two Auger electrons resulting from the double core hole relaxation. A theoretical model is proposed providing absolute photoionization cross sections and revealing clear signatures of direct (monopolar) and conjugate (dipolar near-edge x-ray absorption fine structure) shakeup lines of comparable magnitude.

Roadmap of ultrafast x-ray atomic and molecular physics

Abstract: X-ray free-electron lasers (XFELs) and table-top sources of x-rays based upon high harmonic generation (HHG) have revolutionized the field of ultrafast x-ray atomic and molecular physics, largely due to an explosive growth in capabilities in the past decade. XFELs now provide unprecedented intensity (1020 W cm-2) of x-rays at wavelengths down to ∼1 Angstrom, and HHG provides unprecedented time resolution (∼50 attoseconds) and a correspondingly large coherent bandwidth at longer wavelengths. For context, timescales can be referenced to the Bohr orbital period in hydrogen atom of 150 attoseconds and the hydrogen-molecule vibrational period of 8 femtoseconds; wavelength scales can be referenced to the chemically significant carbon K-edge at a photon energy of ∼280 eV (44 Angstroms) and the bond length in methane of ∼1 Angstrom. With these modern x-ray sources one now has the ability to focus on individual atoms, even when embedded in a complex molecule, and view electronic and nuclear motion on their intrinsic scales (attoseconds and Angstroms). These sources have enabled coherent diffractive imaging, where one can image non-crystalline objects in three dimensions on ultrafast timescales, potentially with atomic resolution. The unprecedented intensity available with XFELs has opened new fields of multiphoton and nonlinear x-ray physics where behavior of matter under extreme conditions can be explored. The unprecedented time resolution and pulse synchronization provided by HHG sources has kindled fundamental investigations of time delays in photoionization, charge migration in molecules, and dynamics near conical intersections that are foundational to AMO physics and chemistry. This roadmap coincides with the year when three new XFEL facilities, operating at Angstrom wavelengths, opened for users (European XFEL, Swiss-FEL and PAL-FEL in Korea) almost doubling the present worldwide number of XFELs, and documents the remarkable progress in HHG capabilities since its discovery roughly 30 years ago, showcasing experiments in AMO physics and other applications. Here we capture the perspectives of 17 leading groups and organize the contributions into four categories: ultrafast molecular dynamics, multidimensional x-ray spectroscopies; high-intensity x-ray phenomena; attosecond x-ray science.

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.

Ultra-fast and ultra-intense x-ray sciences: first results from the Linac Coherent Light Source free-electron laser

Abstract: X-ray free-electron lasers (FELs) produce femtosecond x-ray pulses with unprecedented intensities that are uniquely suited for studying many phenomena in atomic, molecular, and optical (AMO) physics. A compilation of the current developments at the Linac Coherent Light Source (LCLS) and future plans for the LCLS-II and Next Generation Light Source (NGLS) are outlined. The AMO instrumentation at LCLS and its performance parameters are summarized. A few selected experiments representing the rapidly developing field of ultra-fast and peak intensity x-ray AMO sciences are discussed. These examples include fundamental aspects of intense x-ray interaction with atoms, nonlinear atomic physics in the x-ray regime, double core-hole spectroscopy, quantum control experiments with FELs and ultra-fast x-ray induced dynamics in clusters. These experiments illustrate the fundamental aspects of the interaction of intense short pulses of x-rays with atoms, molecules and clusters that are probed by electron and ion spectroscopies as well as ultra-fast x-ray scattering.

Highly Accurate Prediction of Core Spectra of Molecules at Density Functional Theory Cost: Attaining Sub-electronvolt Error from a Restricted Open-Shell Kohn–Sham Approach

Abstract: We present the use of the recently developed square gradient minimization (SGM) algorithm for excited-state orbital optimization to obtain spin-pure restricted open-shell Kohn-Sham (ROKS) energies for core excited states of molecules. The SGM algorithm is robust against variational collapse and offers a reliable route to converging orbitals for target excited states at only 2-3 times the cost of ground-state orbital optimization (per iteration). ROKS/SGM with the modern SCAN/ωB97X-V functionals is found to predict the K-edge of C, N, O, and F to a root mean squared error of ∼0.3 eV. ROKS/SGM is equally effective at predicting L-edge spectra of third period elements, provided a perturbative spin-orbit correction is employed. This high accuracy can be contrasted with traditional time-dependent density functional theory (TDDFT), which typically has greater than 10 eV error and requires translation of computed spectra to align with experiment. ROKS is computationally affordable (having the same scaling as ground-state DFT and a slightly larger prefactor) and can be applied to geometry optimizations/ab initio molecular dynamics of core excited states, as well as condensed phase simulations. ROKS can also model doubly excited/ionized states with one broken electron pair, which are beyond the ability of linear response based methods.

Pulse Duration of Seeded Free-Electron Lasers

Abstract: Paola Finetti, Hauke Höppner, Enrico Allaria, Carlo Callegari, Flavio Capotondi, Paolo Cinquegrana, Marcello Coreno, Riccardo Cucini, Miltcho B. Danailov, Alexander Demidovich, Giovanni De Ninno, Michele Di Fraia, Raimund Feifel, Eugenio Ferrari, Lars Fröhlich, David Gauthier, Torsten Golz, Cesare Grazioli, Yun Kai, Gabor Kurdi, Nicola Mahne, Michele Manfredda, Nikita Medvedev, Ivaylo P. Nikolov, Emanuele Pedersoli, Giuseppe Penco, Oksana Plekan, Mark J. Prandolini, Kevin C. Prince, Lorenzo Raimondi, Primoz Rebernik, Robert Riedel, Eleonore Roussel, Paolo Sigalotti, Richard Squibb, Nikola Stojanovic, Stefano Stranges, Cristian Svetina, Takanori Tanikawa, Ulrich Teubner, Victor Tkachenko, Sven Toleikis, Marco Zangrando, Beata Ziaja, Franz Tavella, and Luca Giannessi Elettra-Sincrotrone Trieste S.C.p.A, 34149 Basovizza, Trieste, Italy Deutsches Elektronen-Synchrotron, Notkestraße 85, 22607 Hamburg, Germany Institut für Physik, Carl von Ossietzky Universität, 26111 Oldenburg, Germany Institut für Laser und Optik, Hochschule Emden/Leer-University of Applied Sciences, Constantiaplatz 4, 26723 Emden, Germany CNR-ISM, 34139 Basovizza, Trieste Italy Laboratory of Quantum Optics, University of Nova Gorica, Nova Gorica 5001, Slovenia Department of Physics, University of Trieste, 34127 Trieste, Italy University of Gothenburg, Department of Physics, Origovägen 6B,412 96 Gothenburg, Sweden Department of Chemical and Pharmaceutical Sciences, University of Trieste, 34127 Trieste, Italy Center for Free-Electron Laser Science/Deutsches Elektronen-Synchrotron DESY, Notkestraße 85, 22607 Hamburg, Germany Department of Radiation and Chemical Physics, Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 182 21 Prague 8, Czech Republic Laser Plasma Department, Institute of Plasma Physics, Czech Academy of Sciences, Za Slovankou 3, 182 00 Prague 8, Czech Republic Helmholtz-Institut Jena, Fröbelstieg 3, 07743 Jena, Germany Class 5 Photonics GmbH, Notkestraße 85, 22607 Hamburg, Germany Molecular Model Discovery Laboratory, Department of Chemistry and Biotechnology, Swinburne University of Technology, Melbourne, 3122, Australia CNR-IOM, Laboratorio Nazionale TASC, 34149 Basovizza, Trieste, Italy Dipartimento di Chimica e Tecnologie del Farmaco, Università la Sapienza, 00185 Roma, Italy Graduate School of Nanotechnology, University of Trieste, 34127 Trieste, Italy Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31-142 Krakow, Poland SLAC National Accelerator Laboratory, 2575 Sand Hill Road, California 94025, USA ENEA, via Enrico Fermi 45, 00044 Frascati Roma, Italy (Received 21 December 2016; published 16 June 2017)