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The pi-pi* and n-pi* valence excited states of dibenzo-p-dioxin (DD) were studied through the complete active space SCF and multiconfigurational second-order perturbation theory employing the cc-pVDZ basis set and full pi-electron active space of 16 electrons in 14 active orbitals. Studies into dependence of the oscillator strengths on the extent of the butterfly-like folding showed that the electronic spectrum is more consistent with a folded equilibrium geometry assumed by DD in solution.

A combination of the multiconfigurational complete active space self-consistent field (CASSCF) and density functional theory (DFT) is employed to study the minimum structures, harmonic vibrational frequencies and electronic spectra of dibenzofuran (DF) and its polychlorinated derivatives. The comparison of the electron transitions in DFs and dioxins reveal various dissimilarities in the origin of the singlet states and a great analogy of the triple states.

A theoretical investigation into unimolecular decomposition paths of primary (POZF) and secondary (SOZF) fluorozonide is carried out by utilizing the multiconfigurational complete active space self-consistent field (CASSCF)/cc-pVTZ level in optimizations of the stationary points and calculations of the harmonic vibrational frequencies.

A detailed study was conducted to investigate the reaction mechanisms and regioselectivity of ethene, fluoroethene and chloroethene reactions with hydroxyl (OH) radicals. Four stationary points were found along the MEP and geometries were optimized while vibrational frequencies were calculated at the UMP2/6-311+G(2d.p) level of theory. Structures of pre-reaction complexes determined at the reactant side of the MEP are characterized by the weak interaction between the hydrogen atom the OH radical and the pi electron density.