Dynamics of photo-activated Coulomb complexes

Intense light with frequencies above typical atomic or molecular ionization potentials as provided by free-electron lasers couples many photons into extended targets such as clusters and biomolecules. This implies, in contrast to traditional multi-photon ionization, multiple single-photon absorption. Thereby, many electrons are removed from their bound states and either released or trapped if the target charge has become sufficiently large. We develop a simple model for this photo activation to study electron migration and interaction. It satisfies scaling relations which help to relate quite different scenarios. To understand this type of multi-electron dynamics on very short time scales is vital for assessing the radiation damage inflicted by that type of radiation and to pave the way for coherent diffraction imaging of single molecules.Comment: 14 pages, 6 figures, 1 tabl

Auger-induced charge migration

Novel perspectives of controlling molecular systems have recently arisen from the possibility of generating attosecond pulses in the ultraviolet regime and tailoring electron dynamics in its natural time scale. The cornerstone mechanism is the so-called charge migration, he production of a coherent charge transfer with subfemtosecond oscillations across a molecule. Typically, charge migration is induced by the ionization of valence molecular orbitals. However, recent technological developments allow the generation of attosecond pulses in the x-ray regime. In this case, the absorption of photons creates core-hole states. In light elements, core-hole states mainly decay by Auger processes that, driven by electron correlations, involve valence orbitals. We theoretically demonstrate in a fluoroacetylene molecule a double-hole charge migration triggered by attosecond core-electron photoionization, followed by Auger electron relaxations. This opens a new route for inducing with x rays charge transfer processes in the subfemtosecond time scaleThis project has received funding from the European Union’s Horizon 2020 research and innovation programme under Marie Sklodowska-Curie Grant Agreement No. 702565, from Comunidad de Madrid through the TALENTO program with Reference No. 2017-T1/IND-5432, and from the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences through Argonne National Laboratory under Contract No. DE-AC02-06CH11357. We acknowledge support from Junta de Castilla y León (Project No. SA046U16) and MINECO (Grant No. FIS2016- 75652-P). C.H.-G. acknowledges support from a 2017 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundatio

Experimental Verification of the Chemical Sensitivity of Two-Site Double Core-Hole States Formed by an X-ray FEL

We have performed X-ray two-photon photoelectron spectroscopy (XTPPS) using the Linac Coherent Light Source (LCLS) X-ray free-electron laser (FEL) in order to study double core-hole (DCH) states of CO2, N2O and N2. The experiment verifies the theory behind the chemical sensitivity of two-site (ts) DCH states by comparing a set of small molecules with respect to the energy shift of the tsDCH state and by extracting the relevant parameters from this shift.Comment: 11 pages, 2 figure

Ionization dynamics in expanding clusters studied by XUV pump probe spectroscopy

he expansion and disintegration dynamics of xenon clusters initiated by the ionization with femtosecond soft x ray extreme ultraviolet XUV pulses were studied with pump probe spectroscopy using the autocorrelator setup of the Free Electron LASer in Hamburg FLASH facility. The ionization by the first XUV pulse of 92 eV photon energy 8 1012 W cm amp; 8722;2 leads to the generation of a large number of quasi free electrons trapped by the space charge of the cluster ions. A temporally delayed, more intense probe 4 1013 W cm amp; 8722;2 pulse substantially increases a population of nanoplasma electrons providing a way of probing plasma states in the expanding cluster by tracing the average charge of fragment ions. The results of the study reveal a timescale for cluster expansion and disintegration, which depends essentially on the initial cluster size. The average charge state of fragment ions, and thus the cluster plasma changes significantly on a timescale of 1 3 p

Atomistic three-dimensional coherent x-ray imaging of nonbiological systems

We computationally study the resolution limits for three-dimensional coherent x-ray diffractive imaging of heavy, nonbiological systems using Ar clusters as a prototype. We treat electronic and nuclear dynamics on an equal footing and remove the frozen-lattice approximation often used in electronic damage studies. We explore the achievable resolution as a function of pulse parameters (fluence level, pulse duration, and photon energy) and particle size. The contribution of combined lattice and electron dynamics is not negligible even for 2 fs pulses, and the Compton scattering is less deleterious than in biological systems for atomic-scale imaging. Although free-electron scattering represents a significant background, we find that recovery of the original structure is in principle possible with 3 °A resolution for particles of 11 nm diameter

Femtosecond X-ray-induced fragmentation of fullerenes

A new class of femtosecond, intense, short – wavelength lasers – the free-electron laser – has opened up new opportunities to investigate the structure and dynamics in many scientific areas. These new lasers, whose performance keeps increasing, enable the understanding of physical and chemical changes at an atomic spatial scale and on the time scale of atomic motion which is essential for a broad range of scientific fields. We describe here the interaction of fullerenes in the multiphoton regime with the Linac Coherent Light Source (LCLS) X-ray free-electron laser at SLAC National Laboratory. In particular, we report on new data regarding the ionization of Ho3N@C80 molecules and compare the results with our prior C60 investigation of radiation damage induced by the LCLS pulses. We also discuss briefly the potential impact of newly available instrumentation to physical and chemical sciences when they are coupled with FELs as well as theoretical calculations and modeling

From synchrotrons for XFELs : The soft x-ray near-edge spectrum of the ESCA molecule

A predictive understanding of soft x-ray near-edge absorption spectra of small molecules is an enduring theoretical challenge and of current interest for x-ray probes of molecular dynamics. We report the experimental absorption spectrum for the electron spectroscopy for chemical analysis (ESCA) molecule (ethyl trifluoroacetate) near the carbon 1s absorption edge between 285-300 eV. The ESCA molecule with four chemically distinct carbon sites has previously served as a theoretical benchmark for photoelectron spectra and now for photoabsorption spectra. We report a simple edge-specific approach for systematically expanding standard basis sets to properly describe diffuse Rydberg orbitals and the importance of triple excitations in equation-of-motion coupled-cluster calculations of the energy interval between valence and Rydberg excitations