[en] In this PhD thesis, lanthanide and actinide based organometallic complexes are studied using quantum chemistry methods. In a first part, the catalytic properties of organo-lanthanide compounds are evaluated by studying two types of reactions: the catalytic hydro-functionalization of olefins and the polymerisation of polar monomers. The reaction mechanisms are theoretically determined and validated, and the influence of possible secondary non productive reactions is envisaged. A second part focuses on uranium-based complexes. Firstly, the electronic structure of uranium metallocenes is analysed. An analogy with the uranyl compounds is proposed. In a second chapter, two isoelectronic complexes of uranium IV are studied. After validating the use of DFT methods for describing the electronic structure and the reactivity of these compounds, it is shown that their reactivity difference can be related to a different nature of chemical bonding in these complexes. (author)

[en] The Sudbury Neutrino Observatory (SNO) has measured both the total flux and the electron-type flux of active 8B neutrinos from the Sun, demonstrating flavor change and solving the solar neutrino problem. This was carried out in three experimental phases, with different strengths and systematic uncertainties. The final analysis of the SNO data was completed, where a substantial improvement in precision was obtained by performing a joint analysis of the data from all phases. This article presents the combined 3-phase data analysis and its results, that provided the most precise measurement of the total neutrino flux and the θ₁₂ mixing angle

[en] Tests on B–L symmetry breaking models are important probes to search for new physics. One proposed model with Δ(B–L)=2 involves the oscillations of a neutron to an antineutron. In this paper, a new limit on this process is derived for the data acquired from all three operational phases of the Sudbury Neutrino Observatory experiment. The search concentrated on oscillations occurring within the deuteron, and 23 events were observed against a background expectation of 30.5 events. These translated to a lower limit on the nuclear lifetime of 1.48 × 10³¹ yr at 90% C.L. when no restriction was placed on the signal likelihood space (unbounded). Alternatively, a lower limit on the nuclear lifetime was found to be 1.18 × 10³¹ yr at 90% C.L. when the signal was forced into a positive likelihood space (bounded). Values for the free oscillation time derived from various models are also provided in this article. Furthermore, this is the first search for neutron-antineutron oscillation with the deuteron as a target.

[en] The presented analysis from the Sudbury Neutrino Observatory (SNO) will combine the photomultiplier tube data from the three phases along with the results from a pulse shape analysis of the data from the Neutral Current Detection (NCD) array used during the third phase to provide the most accurate ⁸B and hep SNO measurements.

[en] Neutrons produced in nuclear interactions initiated by cosmic-ray muons present an irreducible background to many rare-event searches, even in detectors located deep underground. Models for the production of these neutrons have been tested against previous experimental data, but the extrapolation to deeper sites is not well understood. Here we report results from an analysis of cosmogenically produced neutrons at the Sudbury Neutrino Observatory. A specific set of observables are presented, which can be used to benchmark the validity of geant4 physics models. In addition, the cosmogenic neutron yield, in units of 10^–4 cm²/(g•μ), is measured to be 7.28±0.09(stat)${}_{\text{–<!-- ??? -->}1.12}^{+1.59}$(syst) in pure heavy water and 7.30±0.07(stat)${}_{\text{–<!-- ??? -->}1.02}^{+1.40}$(syst) in NaCl-loaded heavy water. These results provide unique insights into this potential background source for experiments at SNOLAB.

[en] Published in summary form only

[en] We compute the optimal microwave field that induces the magnetization reversal of a nanomagnet modeled as a macrospin, while minimizing the total injected energy. Two complementary approaches, numerical and analytical, are presented. We then optimize the microwave field for a nanomagnet with a mixed uniaxial and cubic anisotropy. The optimal microwave fields are found to be modulated both in amplitude and frequency. We find that the cubic anisotropy, which is mainly due here to the surface contribution, has a major effect on the frequency profile, related to the variation of the effective field

[en] The free energies of reaction and the activation energies are calculated, with DFT (B3PW91) and small RECP (relativistic core potential) for uranium, for the reaction of Cp₂UNMe and Cp₂UO with MeC--CMe and H₃Si-Cl that yields the corresponding addition products. CAS(2,7) and DFT calculations on Cp₂UO and Cp₂UNMe give similar results, which validates the use of DFT calculations in these cases. The calculated results mirror the experimental reaction of [1,2,4-(CMe₃)₃C₅H₂]₂UNMe with di-methylacetylene and [1,2,4-(CMe₃)₃C₅H₂]₂UO with Me₃SiCl. The net reactions are controlled by the change in free energy between the products and reactants, not by the activation energies, and therefore by the nature of the UO and UNMe bonds in the initial and final states. A NBO analysis indicates that the U-O interaction in Cp₂UO is composed of a single U-O σ bond with three lone pairs of electrons localized on oxygen, leading to a polarized U-O fragment. In contrast, the U-NMe interaction in Cp₂UNMe is composed of a σ and π component and a lone pair of electrons localized on the nitrogen, resulting in a less polarized UNMe fragment, in accord with the lower electronegativity of NMe relative to O. The strongly polarized U(+)-O(-) bond is calculated to be about 70 kcal mol^-1 stronger than the less polarized U--NMe bond. (authors)

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No abstract available