Imagerie de photoélectrons, sonde de la dynamique (des atomes ... aux adrégats)

Cette thèse concerne l'étude de la désexcitation d'agrégats et d'atomes par imagerie de photoélectrons. La première partie s'intéresse à l'émission thermoïonique d'un système de taille finie. Un dispositif d'imagerie 3D nous permet de mesurer l'évolution temporelle du spectre d'énergie des électrons émis par différents agrégats (Wn-, Cn-, C60). Nous avons alors un accès direct aux quantités fondamentales qui caractérisent cette émission statistique : la température du bain thermique fini et le taux de déclin. La deuxième partie concerne l'ionisation d'états de Rydberg atomiques en présence d'un champ électrique statique. Nous avons réalisé la première expérience de microscopie de photoïonisation qui permet d'obtenir une image qui est la projection macroscopique de la fonction d'onde électronique. Nous avons ainsi accès au détail de la photoïonisation et en particulier aux propriétés quantiques de l'électron habituellement confinées à l'échelle atomiqueLYON1-BU.Sciences (692662101) / SudocSudocFranceF

From Molecular Autoionization to Thermionic Emission.

International audienceAutoionization of Rydberg states and delayed ionization are two decay processes where the excess energy in the molecule or cluster is released by ejecting a free electron. While precise spectroscopic studies of molecular autoionization are commonly performed, allowing a very detailed understanding of the ongoing processes, the study of delayed ionization in clusters is by far less well known and its description is noticeably less precise. Indeed, in complex systems such as clusters, only a statistical approach is found to be relevant as describing the decay dynamics of the system. Beyond these apparent profound differences we show that both phenomena are actually two facets of the same general phenomenon and that delayed ionization, or thermionic emission in clusters, are analogous to molecular autoionization. The transition from autoionization of Rydberg states to delayed ionization, depicted as a transition from a process entirely described within the framework of quantum mechanics to a process described only in the framework of statistical mechanics may further be foreseen as a prototype of the transition from quantum to classical dynamics

Delayed Ionization and Delayed Detachment in Molecules and Clusters

International audienceThe evolution of a molecular system excited above its ionization threshold depends on a number of parameters that include the nature of the excited states and their couplings to the various continua. The general nature of the processes governing this evolution depends also essentially on the complexity of the molecule, more precisely on its size, density of states, and strength of the couplings among the various internal degrees of freedom. In this paper we address the question of the transition between autoionization that prevails in small molecules, and delayed ionization occurring in larger molecules or clusters. This transition is illustrated by autoionization of Na-2 Rydberg states on one hand, delayed ionization in fullerene C-60, and delayed detachment in small cluster anions on the other hand. All processes are studied in the case of nanosecond laser excitation, corresponding to a rather slow deposition of the internal energy

An instrument combining an electrospray ionization source and a velocity-map imaging spectrometer for studying delayed electron emission of polyanions

International audienceAn instrument combining an electrospray ionization source and a velocity-map imaging (VMI) spectrometer has been developed in order to study the delayed electron emission of molecular anions and especially of polyanions. It operates at a high repetition rate (kHz) in order to increase the acquisition speed. The VMI spectrometer has been upgraded for nanosecond time resolution by gating the voltages applied on the position-sensitive detector. Kinetic energy release distribution of thermionic emission (without any contribution from direct detachment) can be recorded for well-defined delays after the nanosecond laser excitation. The capability of the instrument is demonstrated by recording photodetachment spectra of the benchmark C60− anion and C842− dianion

ROLE OF ORGANIC MATTER IN COPPER MOBILITY IN A POLYMICTIC LAKE FOLLOWING COPPER SULFATE TREATMENT (COURTILLE LAKE, FRANCE)

International audienceLake Courtille is a shallow eutrophic polymictic lake treated with copper sulphate for four years. Water column monitoring and laboratory experiments have shown that dissolved copper (CuD) behaviour correlates well with Dissolved Organic Carbon (DOC). Sequential extraction indicates that a significant fraction of the sediment-borne Cu is associated with the organic fraction (50% to 88% of total copper). This fraction of copper could be released into the water column depending on environmental conditions. Laboratory resuspension experiments have shown that significant short term release of Cu was not possible under circumneutral pH and the oxygenated conditions of the lake (less than 3% of the total copper sediment was released). Nevertheless over the long term, a fraction of the copper bound to the sediment could be released depending on the organic matter mineralization which could explain the presence of copper in the water column one year after the last copper addition

XXXI International Conference on Photonic, Electronic,and Atomic Collisions (ICPEAC2019) Proceedings

International audienc

Scintillating Screens Investigations with Proton Beams at 30 keV and 3 MeV

International audienceLuminescent screens hit by accelerated charged particle beams are commonly used as beam diagnostics to produce a visible emitted light, which can be sensed by a camera. In order to investigate the characteristics of the luminescence response of several scintillators, the beam shape and the observation of the transverse position, experiments were done with different low intensity proton beams produced by two different test benches. This study is motivated by the need to identify scintilla-tor materials for the development of a 4-dimensional emittancemeter which will allow the characterization of the beams, in particular the emittance measurement (size, angular divergence). This paper describes the experimental setups and our investigations of the optical properties of various scintillating materials at two different proton beam energies respectively about 30 keV and 3 MeV. The light produced by these screens is characterized by yield, flux of the emitted light versus the beam intensity, time response, and long life-time and they are compared