Rockets, magnetics and spin: a theoretical perspective

The theoretical part of the Dissertation addresses various problems of calculating molecular properties related to the electron spin density at the nuclei. The formalism for analytic evaluation of restricted Hartree-Fock indirect spin-spin coupling constants is reviewed and various aspects of including solvent effects in the calculation of spin-spin coupling are discussed. Suitability of Gaussian basis sets for calculations of properties related to Fermi contact interaction, as well as the electron correlation treatment requirements for such properties are investigated. It is demonstrated, although for the particularly difficult cases of boron and carbon atoms, that very large basis sets and accounting at least to some extent for excitations to all orbitals in the complete space of basis functions may be required to correctly describe spin density at the nuclei. An original derivation of analytic hyperfine coupling tensors for MCQDPT theory is suggested. The derivation is based on the response functions formalism and incorporates some of the earlier results by other authors for analytic MCQDPT energy gradients. Once computed, the hyperfine coupling tensors can be numerically differentiated to obtain indirect spin-spin coupling constants.;The computational part of the Dissertation is a multi-configurational study of mechanisms of reactions of aluminum atoms with oxygen. This study is motivated by potential use of aluminum to improve energetic properties of solid H2 used as a rocket fuel. Our results indicate that the reaction of Al with O2 initially leads to the formation of the AlO2 molecule. A multi-configurational analysis of the PES for AlO2 shows that the linear form of this molecule is considerably lower in energy than the cyclic isomer. AlO2 can dissociate to AlO and atomic oxygen without any barrier beyond the endothermicity of this reaction. There is also no barrier for the reaction of AlO2 with AlO to form Al2O3, and this reaction is highly exothermic. While an additional study of the AlO2 + AlO 2 reaction is still necessary to make the final conclusion, most of our results suggest that Al2O3, may indeed be the main product of the Al combustion