Que peut-on faire avec un noyau quadrupolaire en RMN ? Un exemple avec le cobalt 59

We have observed cobalt 59 NMR on tetrahedric clusters in solution and in the solid state. From the relaxation times in solution, we are able to deduce the quadrupolar coupling constants for 99Ru and to simulate the 59Co spectrum in the solid state for the basal atoms of Co4(CO)12 which has never been observed. This short review shows the interest of high fields applied to quadrupolar nuclei

K-shell double core-hole spectroscopy in molecules

A great deal of attention has been devoted in the last few years to photoionization processes in isolated molecules leading to the formation of double core-hole (DCH) states. There are two main experimental avenues to induce such processes, namely single-photon absorption followed by the simultaneous ejection of two core electrons, and x-ray-induced multiphoton processes leading to the production of DCH states via the sequential absorption of two soft x- ray photons on a time scale on the order of the molecular Auger lifetime (4–8 femtoseconds for light elements). The formation of molecular two-site (ts) DCH states, in particular, shows great potential as a powerful tool for chemical analysis. A compelling motivation for the study of ts-DCH states is their ability to probe the local chemical environment more sensitively than either single core-hole (SCH) or single-site (ss) DCH states. The enhanced sensitivity originates from the fact that the double ionization potential (DIP) of ts-DCH states is directly coupled to induced changes in the valence charge distribution at the two different atomic sites. Here a review of the recent literature is presented on both types of experiments, and on the related theoretical work

Exchange Interaction Effects in NO Core-Level Photoionization Cross-Sections

The effect of the exchange interaction in the photoionization continuum is investigated, using N 1s photoionization of NO into the 1s−12π (1Π) and (3Π) final states as an example. The separation in energy of these two final states is 1.41 eV. Significant differences in their partial photoionization cross-sections are observed over a wide range of energies and cannot be accounted for by the different multiplicity of the states. We suggest that the deviation of the 3Π/1Π cross-section ratio from the statistical weighting at intermediate energies is dominated by the difference in the final-state potential experienced by the photoelectron and at asymptotically high energies by the multiplet-dependent amount of intensity going into multi-electron (shake-up) processes. Calculations underpinning this point are presented. We also show supporting measurements of the 3Π/1Π cross-section ratio for O 1s ionization and the absolute photoabsorption cross-section for NO over a wide energy range covering the core level region