Atoms interacting with a metal surface with adsorbates: local and non-local effects on the charge transfer

A model system representing a collisional Li atom interacting in the “on top” geometry with an Al surface partly covered with Li adsorbates is studied. The cases of a unique adsorbate and of a uniform adsorbate layer are considered and compared. The energies and widths of the atom levels are much modified in the vicinity of the adsorbate. This is interpreted in terms of molecularisation of the atomic and adsorbate levels. These results also determine the relative importance of the local and non-local effects of the adsorbates on the resonant charge transfer process in atom-surface collisions.     

Orbital angular momentum in triatomic molecules

The effects of electronic angular momentum in triatomic linear molecules are considered. An effective vibronic hamiltonian is derived and second order energy level expressions are obtained for the bending levels in an electronic Π state. The formulae allow for the anharmonicity of the bending potentials and for the variation of the expectation value <L_z > with bond angle; effects of electron spins are also included. The vibronic levels predicted by the analytic expressions are compared with those calculated using a full matrix treatment of the orbital angular momentum; it is shown that they are far more accurate than the levels predicted by the formulae currently available in the literature. The relationship between the anharmonic corrections and the deviation of <L_z > from unity is discussed in terms of an electrostatic interaction between linear molecule states of different symmetry.     

Transient kinetic studies involving exciplex formation. Methods of analysis

In this paper, rate parameters are extracted from fluorescene decay data in the framework of Feedback-Type Kinetics (k₈ < k₄). The exciplex dissociation (k₄) and fluorescene decay rate constants (k₈) have been obtained for the five following systems: For this task we have added to the straight line method of Ware which is valid in certain cases only at high perturber concentrations, a new but similar Taylor series method applicable at low concentrations. Thereafter, a safer and more general method of kinetic analysis based on a quasi-linear χ² minimization procedure has been developed and applies to data in any range of concentration.     

Modèle de comportement mécanique du béton armé corrodéMechanical model of reinforced concrete damaged by steel corrosion

This article deals with an analytical mechanical model of reinforced concrete damaged by steels corrosion. It is based on the taking into account of local bond between steel and the tensile concrete located between the cracks. Then, this model allows to quantify the coupled effect of steel cross section reduction and loss of bond strength due to steel corrosion on mechanical behaviour of reinforced concrete. To cite this article: A. Castel et al., C. R. Mecanique 330 (2002) 45–50     

Wedelolides A and B: novel sesquiterpene delta-lactones, (9R)-eudesman-9,12-olides, from Wedelia trilobata

Two new sesquiterpene lactones, wedelolides A (1) and B (2), were isolated by bioassay-guided fractionation from the leaves of Wedelia trilobata, together with known trilobolides 6-O-isobutyrate (3) and 6-O-methacrylate (4). The compounds 1 and 2 were the first examples of an unprecedented framework: a novel sesquiterpene delta-lactone, (9R)-eudesman-9,12-olide. The structures of the antimalarial wedelolides A (1) and B (2) were determined on the basis of MS and 2D NMR spectral analysis. The absolute configuration of eight carbon stereocenters of compounds 1 and 2 was determined to be 1S,4S,5S,6R,7S,8S,9R,10S by mean of auxiliary chiral MTPA derivatives.     

Synthesis and Placental Binding Potencies of Photosensitive Analogues of Luteinizing Hormone Releasing Hormone (LHRH) with Agonistic and Antagonistic Structures

The synthesis of new photolabeling analogues of luteinizing hormone releasing hormone is described. Peptides were prepared by the solid-phase method, and the photolabeling moiety was introduced as the 4′-nitrophenyl-alanine precursor. This amino acid, either of the L or D configuration, was placed at different positions and was modified afterwards to 4′-azidophenylalanine. Structures with agonistic or antagonistic character were prepared, together with a peptide containing simultaneously the photolabeling moiety and a biotin substituent for future receptor isolations. Binding studies on placental and pituitary membranes indicate that these compounds represent promising candidates for receptor labeling studies.     

Pure rotational spectrum of PH3 in the 10–100 cm−1 range: Collisional broadening coefficients by H2 and He

The H₂- and He-broadened widths have been measured at room temperature for seven pure rotational lines of phosphine in the spectral range 10–80 cm^–1. The retrieval of linewidths values was carried out, on the assumption of identical linewidths for theJ+1K-components within a given multipletJ+1J. The results obtained are in good agreement with the previous determination reported for the 10 line, in the microwave range.