Photodissociation de NO

La fluorescence de NO* produit par photodissociation de NO2 a été étudiée en fonction de la longueur d’onde d’excitation dans le domaine 110-140 nm au moyen du rayonnement synchrotron de LURE ACO. Le spectre d’excitation de la fluorescence globale du fragment NO* reproduit le spectre d’absorption de NO2 dans cette région. Les spectres de fluorescence obtenus en excitant N02 dans la bande d’absorption située entre 131 et 125 nm ainsi qu’à 123,6 nm avec la raie de résonance du krypton sont diffus à cause de la superposition des émissions provenant de NO A2Σ+ et B2Π. Deux bandes de fluorescence distinctes ont pu être attribuées aux niveaux NO A (v’ = 2,1). Les mesures de durée de vie de NO Av’ = 1 confirment cette attribution. La population relative de ces deux niveaux est constante dans le domaine 120-130 nm. Un rapport de branchement constant NO A/B = 1 a également pu être évalué dans la même région

Observation of the first vibrations of the newly born Cs–CH

The femtosecond photodissociation of CsI in the CsI–CH3CN complex has been studied. Recurrences are observed in the detection of the Cs+–CH3CN ion complex. They are assigned to the first vibrations of the Cs–NCCH3 bond formed after the CsI dissociation. This result is in good agreement with calculations on the similar NaI–CH3CN system which predict a linear structure for the ground state complex

Femtosecond time-resolved photoelectron spectra of ammonia molecules and clusters

The first femtosecond pump-probe photoelectron spectroscopy experiment for neutral clusters is reported. The $\widetilde{A}$ state of ammonia molecules and clusters is excited with 120 fs pulses at 200 nm and probed by ionisation at 267 or 400 nm. Ions and electrons are detected in coincidence. The high repetition rate of the fs laser allows one to reduce the coincidence rate per laser pulse to less than 0.05 per pulse so that photoelectrons and photoions can be correlated unambiguously. The energy flow in the excited neutral cluster states is followed in real time, and the energy content in the ionic clusters can be related to the fragmentation patterns

Photodissociation dynamics of Cl

The photodissociation of a chlorine molecule in the environment of a xenon cluster has been studied experimentally using the real time pump and probe technique through the formation of an XeCl reaction product. The photodissociating system is probed in such a way that the movement of a single chlorine atom in the xenon environment is detected. Various XenCl2 cluster sizes have been investigated leading to the distinction between uncapped, half-capped and doubly capped structures for these clusters. These structures have a profound influence on the photodissociation dynamics. Retrapping of one chlorine atomic fragment and stabilization of the XeCl reaction product is only observed for the half and doubly capped clusters. The experimental work is complemented by classical molecular dynamics calculations to get a full picture of the photodissociation

Photoionization of NaI: inward-outward asymmetry in the wave packet detection

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Improving the purification of membrane proteins from Escherichia coli C41(DE3)

The overexpression and purification of membrane proteins to high purity and homogeneity is a challenging task. Over time, several strains have been developed that decrease the toxic side-effects and thus result in higher bio mass and protein yield. However, two major contaminants have been identified in membrane protein preparations from E. coli: the outer membrane porin OmpF and AcrB, which is part of a tripartite efflux pump. Both proteins crystallise from low concentrations and diverse conditions, which make them a major problem, especially in membrane protein crystallography. In this study, we present a C41(DE3)-derived expression strains that is depleted of these two proteins