Publications de Wojciech Gawelda

Spin cascade and doming in ferric hemes: Femtosecond X-ray absorption and X-ray emission studies

Majed Chergui, Wojciech Gawelda, Christopher Alexander Arrell, Frederico Alves Lima, Giulia Fulvia Mancini, Dominik Kinschel, Oliviero Cannelli, Camila Bacellar Cases Da Silveira, Rebecca Ann Ingle, Jérémy Raymond Jean Maurice Rouxel, Samuel Menzi

The structure-function relationship is at the heart of biology, and major protein deformations are correlated to specific functions. For ferrous heme proteins, doming is associated with the respiratory function in hemoglobin and myoglobins. Cytochrome c (C ...

National Academy of Sciences2020

Revealing hole trapping in zinc oxide nanoparticles by time-resolved X-ray spectroscopy

Majed Chergui, Wojciech Gawelda, Thomas James Penfold, Jochen Rittmann, Fabio Giacomo Santomauro

Nature Research2018

Revealing hole trapping in zinc oxide nanoparticles by time-resolved X-ray spectroscopy

Majed Chergui, Wojciech Gawelda, Thomas James Penfold, Jochen Rittmann, Fabio Giacomo Santomauro

AMER CHEMICAL SOC2018

Time-resolved x-ray absorption spectroscopy: Watching atoms dance

Majed Chergui, Paul Beaud, Wojciech Gawelda, Camelia Borca, Amal El Nahhas, Van Thai Pham, Renske Marjan van der Veen, Frederico Alves Lima

The introduction of pump-probe techniques to the field of x-ray absorption spectroscopy (XAS) has allowed the monitoring of both structural and electronic dynamics of disordered systems in the condensed phase with unprecedented accuracy, both in time and i ...

Iop Publishing Ltd, Dirac House, Temple Back, Bristol Bs1 6Be, England2009

Structural analysis of ultrafast extended x-ray absorption fine structure with subpicometer spatial resolution : Application to spin crossover complexes

Majed Chergui, Wojciech Gawelda, Van Thai Pham, Renske Marjan van der Veen

We present a novel analysis of time-resolved extended x-ray absorption fine structure (EXAFS) spectra based on the fitting of the experimental transients obtained from optical pump/x-ray probe experiments. We apply it to the analysis of picosecond EXAFS da ...

2009

Femtosecond XANES Study of the Light-Induced Spin Crossover Dynamics in an Iron(II) Complex

Majed Chergui, Paul Beaud, Wojciech Gawelda, Camelia Borca, Amal El Nahhas, Van Thai Pham, Renske Marjan van der Veen

X-ray absorption spectroscopy is a powerful probe of mol. structure, but it has previously been too slow to track the earliest dynamics after photoexcitation. We investigated the ultrafast formation of the lowest quintet state of aq. iron(II) tris(bipyridi ...

American Association for the Advancement of Science2009

Retrieving photochemically active structures by time-resolved EXAFS spectroscopy

Majed Chergui, Wojciech Gawelda, Camelia Borca, Amal El Nahhas, Van Thai Pham, Renske Marjan van der Veen, Frederico Alves Lima

Describing the nature and structure of molecular excited states is important in order to understand their chemical reactivity and role as intermediates in photochemical reactions. The recent implementation of x-ray absorption spectroscopy in the ultrafast ...

Iop Publishing Ltd, Dirac House, Temple Back, Bristol Bs1 6Be, England2009

Relaxation processes of point defects in vitreous silica from femtosecond to nanoseconds

Majed Chergui, Frank van Mourik, Wojciech Gawelda, Erwin Portuondo Campa, Andrea Cannizzo, Andrea Callegari

The authors studied ultrafast relaxation of localized excited states at Ge-related O deficient centers in SiO2 using femtosecond transient-absorption spectroscopy. The relaxation dynamics exhibits a biexponential decay, which the authors ascribe to the dep ...

2008

Light-induced spin crossover probed by ultrafast optical and X-ray spectroscopies

Majed Chergui, Wojciech Gawelda, Amal El Nahhas, Andrea Cannizzo, Van Thai Pham, Renske Marjan van der Veen

The photoinduced energy and structural relaxation of aq. iron(II)-tris-bipyridine ([FeII(bpy)3]2+), upon excitation into its singlet metal-to-ligand charge transfer (1MLCT) band, and the population of its short-lived (?0.6 ns) high-spin excited state have ...

2007

Ultrafast Nonadiabatic Dynamics of [FeII(bpy)3]2+ in Solution

Majed Chergui, Frank van Mourik, Wojciech Gawelda, Andrea Cannizzo, Van Thai Pham

The ultrafast relaxation of aq. Fe(II)-tris(bipyridine) upon excitation into the singlet metal-to-ligand charge-transfer band (1MLCT) was characterized by femtosecond fluorescence up-conversion and transient absorption (TA) studies. The fluorescence expt. ...

2007

Structural Determination of a Short-Lived Excited Iron(II) Complex by Picosecond X-Ray Absorption Spectroscopy

Majed Chergui, Wojciech Gawelda, Van Thai Pham

Structural changes of the Fe(II)-tris-bipyridine ([FeII(bpy)3]2+) complex induced by ultrashort pulse excitation and population of its short-lived (?0.6 ns) quintet high spin state were detected by picosecond x-ray absorption spectroscopy. The structural r ...

2007

Capturing transient electronic and molecular structures in liquids by picosecond X-ray absorption spectroscopy

Majed Chergui, Wojciech Gawelda, Amal El Nahhas, Van Thai Pham

We describe an advanced setup for time-resolved x-ray absorption fine structure (XAFS) spectroscopy with picosecond temporal resoln. It combines an intense femtosecond laser source synchronized to the x-ray pulses delivered into the microXAS beamline of th ...

2007

Observation of the Solvent Shell Reorganization around Photoexcited Atomic Solutes by Picosecond X-ray Absorption Spectroscopy

Majed Chergui, Wojciech Gawelda, Van Thai Pham

We report on the observation of the solvation shell rearrangement after abstraction of the electron from aq. I- in a laser pump/X-ray probe expt. by recording the X-ray absorption L1- and L3-edge spectra, 50 ps after laser excitation. The L1-edge spectra c ...

2007

Electronic and Molecular Structure of Photoexcited [RuII(bpy)3]2+ Probed by Picosecond X-ray Absorption Spectroscopy

Majed Chergui, Wojciech Gawelda

L2,3 x-ray absorption spectra of aq. [RuII(bpy)3]2+ were recorded in its ground and excited states, 50 ps after short pulse laser excitation. Significant changes in both the XANES (x-ray Near-Edge Absorption Structure) and the EXAFS (Extended x-ray Absorpt ...

2006

Time-resolved x-ray absorption spectroscopy of transition metal complexes

Wojciech Gawelda

Electronic structure changes are at the origin of the making, breaking and transformation of bonds. These changes can be visualized by measuring the geometric structure in "real-time" during the course of a chemical reaction, a biological function or a phy ...

EPFL2006

Photexcitation of Aqueous Ruthenium(II)-tris-(2,2'-bipyridine) with High-Intensity Femtosecond Laser Pulses

Majed Chergui, Wojciech Gawelda

The authors report a femtosecond pump-probe study of photochem. of concd. aq. solns. of [Ru(bpy)3]2+, as a function of pump power (up to 2 TW/cm2) at 400 nm excitation. The transient absorption spectra in the 345-660 nm range up to 1 ns time delay enable t ...

2006

A Full Multiple Scattering Model for the Analysis of Time-Resolved X-ray Difference Absorption Spectra

Majed Chergui, Wojciech Gawelda

A full multiple theor. model (MXAN) is applied to fit picosecond difference x-ray absorption spectra at the Ru L3 edge upon photoexcitation of aq. [RuII(bpy)3]2+. Fitting difference spectra allows an increase in sensitivity, such that slight structural cha ...

2006

Broadband femtosecond fluorescence spectroscopy of [Ru(bpy)3]2+

Majed Chergui, Frank van Mourik, Wojciech Gawelda, Goran Zgrablic, Andrea Cannizzo

Femtosecond fluorescence-upconversion studies of aq. [Ru(bpy)3]2+ show a short-lived vibrationally hot emission of the singlet metal-to-ligand charge-transfer state, with an ultrafast intersystem crossing (~ 10 fs) to the triplet state at const. energy (th ...

Wiley-VCH Verlag GmbH2006

Picosecond time-resolved X-ray Absorption Spectroscopy of solvated organometallic complexes

Majed Chergui, Wojciech Gawelda, Melanie Saes

We describe an experimental setup, which measures transient chemical changes of photoexcited solutes in disordered systems via time-resolved X-ray Absorption Spectroscopy (XAS) with picosecond temporal resolution. The setup combines a femtosecond amplified ...

2005