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The 1s −2 Auger hypersatellite spectrum of argon is studied experimentally and theoretically. In total, three transitions to the final states 1s −12p −2(2 S e ,2 D e ) and 1s −12s −1(1 S)2p −1(2 P o ) are experimentally observed. The lifetime broadening of the 1s −2 → 1s −12p −2(2 S e ,2 D e ) states is determined to be 2.1(4) eV. For the used photon energy of hν = 7500 eV a KK/K ionisation ratio of 2.5(3) × 10−4 is derived. Generally, a good agreement between the experimental and present theoretical energy positions, linewidths, and intensities is obtained.

We have investigated nonlinear processes in small molecules by x-ray photoelectron spectroscopy using the Linac Coherent Light Source free electron laser, and by simulations. The main focus of the experiments was the formation of the two-site double core-hole (tsDCH) states in the molecules CO2, N2O and N-2. These experiments are described in detail and the results are compared with simulations of the photoelectron spectra. The double core-hole states, and in particular the tsDCH states, have been predicted to be highly sensitive to the chemical environment. The theory behind this chemical sensitivity is validated by the experiments. Furthermore, our simulations of the relative integrated intensities of the peaks associated with the nonlinear processes show that this type of simulation, in combination with experimental data, provides a useful tool for estimating the duration of ultra-short x-ray pulses.

International audience; We report on an experimental investigation of 1.04 MeV H + +N2 electron transfer collisions. The fast protons were stored in the electron-cooler ion-storage ring, CRYRING and the molecular nitrogen target was provided with a supersonic gas jet. We report momentum distributions of atomic nitrogen dissociation products N q+ with charge states q+ (q=1, 2, 3) which are detected in coincidence with neutralized projectiles. Further, we investigate the influence of the angle between the direction of the incoming projectile beam and the target molecular axis. The orientation of the latter is determined from the momentum vector of one emitted atomic nitrogen fragment ion. We find significantly higher total yields, dominated by N +, of charged atomic dissociation products when the N2 molecular axis is perpendicular to the incoming H + -beam. The relative contributions from N 2+- and N 3+- fragments, however, are strongest when the N2 axis is aligned--or close to aligned--with the ion beam. This, we suggest, is due to increased probabilities for formation of two-site double-core-hole states.

Multiconfiguration expansions frequently target valence correlation and correlation between valence electrons and the outermost core electrons. Correlation within the core is often neglected. A large orbital basis is needed to saturate both the valence and core-valence correlation effects. This in turn leads to huge numbers of configuration state functions (CSFs), many of which are unimportant. To avoid the problems inherent to the use of a single common orthonormal orbital basis for all correlation effects in the multiconfiguration Hartree-Fock (MCHF) method, we propose to optimize independent MCHF pair-correlation functions (PCFs), bringing their own orthonormal one-electron basis. Each PCF is generated by allowing single- and double-excitations from a multireference (MR) function. This computational scheme has the advantage of using targeted and optimally localized orbital sets for each PCF. These pair-correlation functions are coupled together and with each component of the MR space through a low dimension generalized eigenvalue problem. Nonorthogonal orbital sets being involved, the interaction and overlap matrices are built using biorthonormal transformation of the coupled basis sets followed by a counter-transformation of the PCF expansions. Applied to the ground state of beryllium, the new method gives total energies that are lower than the ones from traditional complete active space (CAS)-MCHF calculations using large orbital active sets. It is fair to say that we now have the possibility to account for, in a balanced way, correlation deep down in the atomic core in variational calculations. © 2010 IOP Publishing Ltd., SCOPUS: ar.j, info:eu-repo/semantics/published

Energy levels, fine-structure separations, specific mass shift parameters, isotope shifts, hyperfine interaction constants, Lande gJ-factors and transition probabilities are reported for the 2s22p2–2s2p3 transition array in N II, O III, F IV, Ne V and Ti XVII. Wavefunctions were determined using the multiconfiguration Dirac–Hartree–Fock method with account for valence, core-valence and core–core correlation effects. The transition energies and rates are compared with experimental data and with values from other calculations.

Hyperfine quenching rates of the 3s3p3P0 level in Mg-like ions were calculated using the GRASP2K package based on the multi-configuration Dirac–Hartree–Fock method. Valence and core-valence correlation effects were accounted for in a systematic way. Breit interactions and QED effects were included in the subsequent relativistic CI calculations. Calculated rates were compared with other theoretical values and with experiment, and a good agreement with the latest experimental value for the ion (Rosenband et al 2007 Phys. Rev. Lett. 98 220801) was found. Furthermore, we showed in detail the contributions from Breit interaction and QED effects to concerned physical properties. Finally, electronic data were presented in terms of a general scaling law in Z that, given isotopic nuclear spin and magnetic moment, allows hyperfine-induced decay rates to be estimated for any isotope along the isoelectronic sequence.