engleski

Theoretical Study of Structure, Vibrational Frequencies and Electronic Spectra of Dibenzofuran and its Polychlorinated Derivatives

Minimum structures and harmonic vibrational frequencies of dibenzofuran (DF), 2, 3, 7, 8-tetrachlorodibenzofuran (TCDF) and octachlorodibenzofuran (OCDF) were calculated using the multiconfigurational complete active space SCF (CASSCF) and density functional theory (DFT) methods. The electronic transitions in these compounds were studied via the single state multireference second order perturbation theory (CASPT2) based on the CASSCF(14, 13) references, as well as the time dependent DFT (TD-B3P86) employing the cc-pVDZ (CASSCF/CASPT2) and 6-31G(d, p) (TD-B3P86) basis sets. The B3P86 geometry and harmonic vibrational frequencies of the ground state DF agree very well with the experimental data, and the CASSCF/CASPT2 excitation energies and oscillator strengths are accurate enough to provide a reliable assignment of the absorption bands in the 200-300 nm region. The close agreements with experiment for the parent DF give the present theoretical approaches a valuable credit in predicting the properties of the environmentally toxic polychlorinated congeners, which is all the more important considering difficulties and hazards in obtaining the experimental data.

Ab Initio methods; CASSCF/CASPT2; Density Functional Theory; polychlorinated dibenzofurans; structure; vibrational spectrum; electronic spectrum

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