Relationship of moleculated radical anion abundance and calculated lowest unoccupied molecular orbital energies for polychlorinated dibenzofurans and dibenzodioxins in electron capture negative ion mass spectrometry: Evidence for negative metastable ions

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Abstract
Relationships were found between experimentally measured molecular radical anion abundances and calculated lowest unoccupied molecular orbital energies (εLUMO) for polychlorodibenzofurans and polychlorodibenzo-p-dioxins. Anion abundances were measured using standard using standard mass spectrometric techniques, while εLUMO were calculated by the ‘Complete Neglect of Differential Overlap’ method. Polychlorodibenzofurans with calculated εLUMO ≥ 1.6 eV show 0% molecular radical anion and those with εLUMO ≤ 1.4 eV show ≥ 80% molecular radical anion abundance. Similarly, the molecular radical anion is absent for polychlorodibenzo-p-dioxins with calculated εLUMO ≥ 2.0 eV. A trend towards greater molecular radical ion relative abundance appears for 2.0 eV εLUMO ≥ 1.0 eV and a maximum is reached around 1 eV, whereupon the molecular ion abundance diminishes with lower εLUMO. B/E linked scan analysis indicates that chlorodioxins with εLUMO < 1 eV give increasing amounts of metastable anions.