Publications de Majed Chergui | EPFL Graph Search

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We report on structural dynamics in simple van der Waals solids (Ar, Ne, and H2), as driven by the excitation of an impurity (NO) Rydberg state. The resulting charge redistribution induces a local radial deformation of the medium ("bubble" formation). This process can be characterized by steady-state spectroscopy and analyzed within the framework of the configuration coordinate model and harmonic approxn. Intermol. potentials describing the impurity-medium interaction are obtained, allowing us to establis

The ability to visualize molecular structure in the course of a chemical reaction or a biological function has been a dream of scientists for decades. X-ray absorption spectroscopy (XAS) is ideal in this respect because it is chemically selective and can be implemented in any type of medium. Furthermore, using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) in laser pump/X-ray probe experiments allows the retrieval of not only the local geometric structure o

The term values of the ground and excited Rydberg states of alkali metal atoms trapped in rare gas matrixes were derived from an empirical model potential. The anal. potential smoothly connects the Coulomb potential near the core with the shielded Coulomb potential beyond the first shells of surrounding matrix atoms. The potential does not depend on the specific dopant, and is detd. for each rare gas matrix in a unique way from the polarization energy of the crystal by the ionic core P+ and from the electro

In a seminal paper, Mahan predicted that excitonic bound states can still exist in a semiconductor at electron-hole densities above the insulator-to-metal Mott transition. However, no clear evidence for this exotic quasiparticle, dubbed Mahan exciton, exis ...

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 ...

Although, ferrous hemeproteins dynamics and ligand photodissocn. pathways has been discussed, less is known about the ferric hemeproteins photophys. processes. Recently, ultrafast timescale measurements of ferric HbICN (Hb I from L. pectinata) and MbCN complexes indicated the presence of a short-lived absorption signal, which developed into a red shifted Soret band and decays to zero with time const. in 3.6 ps. Data presented here on ferric HbINO, HbIN3, HbIH2S and metHbI and ferrous HbICN and HbINO complex

Low-temp. gas-phase wavelengths and bandwidths for astronomical searches for C60 in the 2400-4100 Å region are detd. from the absorption spectra of C60 in rare gas matrixes at 4 K, coupled with information on the dependence of the vibronic transition frequencies of this fullerene on the Lorentz-Lorenz polarizability parameter of matrixes and solvents. These bandwidths increase from 25 +- 5 cm-1 for the 1 1T1u-1 1Ag band at 4024.0 +- 0.5 Å to 2300 +- 200 cm-1 for the 6 1T1u-1 1Ag band at 2488 +- 8 Å. Spectra

Ferrous iron(II) hexacyanide in aqueous solutions is known to undergo photoionization and photoaquation reactions depending on the excitation wavelength. To investigate this wavelength dependence, we implemented ultrafast two-dimensional UV transient absor ...

A microscopic, theor., and exptl. description of an elementary solid state photoreaction, i.e. the dissocn. of a small mol. in a rare lattice is presented. The ingredients and results of mol. dynamics calcns. for the dissocn. of F2, Cl2, HI, and H2O mols. are discussed and the concepts of cage effect, impulsive and delayed exit are illustrated. Examples for the detn. of the structure and dynamics of and products in the matrix from ESR, IR and neutron expts. are combined with exptl. investigations of the bar

Dizzy cooling: Femtosecond excitation of the singlet states of aqueous [FeII(bpy)3]2+ (bpy=2,2-bipyridine) leads to the formation of a vibrationally hot quintet state that exhibits wave-packet dynamics arising from a chelate-ring and bending mode. The vibr ...

The cage-induced stabilization of fragments in excited electronic states following the UV-dissocn. of ICN in cryogenic matrixes is discussed. Emission spectra recorded upon ~A-band excitation of ICN in solid Ne, Ar and Kr exhibit a long progression of broad bands due to a weakly bound electronically excited state, presumably one of the low-lying triplet states 3P1 or 3P2 of ICN. A lifetime anal. favors the 3P2 state. Mol. dynamics with quantum transitions (MDQT) simulations were conducted on 6 coupled elect

Highly structured fluorescence and fluorescence excitation spectra of C70 in Ne matrixes are reported. Fluorescence from both S1 and S2 states is obsd., and these are identified as being of A2' and E1' and have energies of 15,524 cm-1 and 15,691 cm-1, resp. A 3rd singlet state is identified in the excitation spectrum and probably is of A2 symmetry with an energy of 15,966 cm-1. [on SciFinder (R)]

The F2 laser emission in Ne matrixes at 160.6 nm is reported for the first time. Its excitation spectrum in the 11-16 eV range has been recorded by means of tunable synchrotron radiation. Anomalous envelopes of vibrational progressions occurring in the gas phase due to avoided crossing of ion-pair 1Su+ states and Rydberg 1Su+ states are shown to disappear in Ne matrixes. The matrix spectra are discussed in terms of a deperturbed C1S+ ion-pair and strongly blue-shifted I1Su+ and H1.product.u Rydberg states.

A visible-pump/UV-probe transient absorption is used to characterize the ultrafast dynamics of bacteriorhodopsin with 80-fs time resoln. We identify three spectral components in the 265- to 310-nm region, related to the all-trans retinal, tryptophan (Trp)- ...

Highly structured fluorescence is reported for C60 mols. isolated in Ne and Ar matrixes. Their excitation spectra are similar to the gas-phase 2-photon ionization spectrum of C60. Most of the bands seen in emission can be attributed to Herzberg-Teller or Jahn-Teller active modes and to combinations of these modes. The intensity distribution of the fluorescence bands is compared with calcd. intensities and shows that the emission is of mixed singlet T1g and T2g character in Ne matrixes in nearly equal propor

The absorption spectra of HCl in rare gas matrixes were recorded in the 1st continuum (A 1P->X 1S+) region in Kr and Xe matrixes and up to 100 nm in Ar matrixes. Concn. and temp. effects were used to distinguish between absorption from monomers and that from clusters. The 1st continuum band of the monomer is seen to shift red by .apprx.0.36 eV in Ar matrixes, while it shifts blue by .apprx.0.3 and .apprx.0.08 eV in Kr and Xe matrixes, resp. Simultaneously, the oscillator strength of the A 1P state increases

Femtosecond white-light continuum probe transient absorption and reflectivity measurements of bulk graphite and graphene paper are reported. In graphite, the relaxation of photoinduced electron–hole pairs happens through in-plane electron–electron and elec ...

The need to visualize molecular structure in the course of a chemical reaction, a phase transformation or a biological function has been a dream of scientists for decades. The development of time-resolved X-ray and electron-based methods is making this tru ...

Several new results and opportunities for ultrafast x-ray absorption spectroscopy (XAS) are demonstrated. It is possible to work with highly dil. solns. in transmission mode without dramatic loss of signal-to-noise ratio. This is very promising as one can envision the study of samples, for which large concns. are impossible to reach. Moreover, it is possible to scan the time delay between the laser pump pulse and the x-ray probe pulse, and therefore follow the evolution of the system from the start. The ope

Picosecond and femtosecond X-ray absorption spectroscopy is used to probe the changes of the solvent shell structure upon electron abstraction of aqueous iodide using an ultrashort laser pulse. The transient L-1,L-3 edge EXAFS at 50 ps time delay points to ...

Majed Chergui

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Impurity Rydberg states as probes of local dynamics in the condensed phase

Molecular Structural Dynamics Probed by Ultrafast X-Ray Absorption Spectroscopy

A model potential for Rydberg states of alkali atoms in rare gas matrixes

Mahan excitons in room-temperature methylammonium lead bromide perovskites

Retrieving photochemically active structures by time-resolved EXAFS spectroscopy

Photophysical Processes of Fe(II) and Fe (III) Hemoglobin I Ligand Complexes of Lucina pectinata

Absorption wavelengths and bandwidths for interstellar searches of C60 in the 2400-4100 Å region

Photoaquation Mechanism of Hexacyanoferrate(II) Ions: Ultrafast 2D UV and Transient Visible and IR Spectroscopies

Photochemistry, charge-transfer states, and laser applications of small molecules in rare gas crystals

Vibrational coherences and relaxation in the high-spin state of aqueous [Fell(bpy)3]2+

Caging and excited state emission of ICN trapped in cryogenic matrixes: experiment and theory

Matrix isolation spectroscopy of C70 - vibrational analysis and assignment of the lowest excited states

VUV luminescence and spectroscopy of F2 in Ne crystals

Insights into excited-state and isomerization dynamics of bacteriorhodopsin from ultrafast transient UV absorption

Fluorescence spectra of isolated C60 molecules in neon and argon matrixes: assignment of the lowest emitting states

Absorption by dissociative continua and Rydberg states in condensed matter: HCl in rare gas matrixes

Femtosecond carrier dynamics in bulk graphite and graphene paper

Picosecond and femtosecond X-ray absorption spectroscopy of molecular systems

Structural dynamics and electronic structure changes probed with lasers and X-rays

Probing the Transition from Hydrophilic to Hydrophobic Solvation with Atomic Scale Resolution