| Summary: | This thesis reports studies of the electronic spectrum of gaseous MnO. The (0,0) band of the A⁶Σ +-X⁶ Σ+ electronic transition of MnO was recorded by intermodulated laser-induced fluorescence over the range 17770 - 17970 cm⁻¹. The hyperfine structure caused by the ⁵⁵Mn nucleus (I = 5/2) is almost completely resolved. Internal hyperfine perturbations between the F₃ and F₄electron spin components (where N = J - 1/2 and N = J + 1/2, respectively) occur in the ground state of MnO. These are caused by hyperfine matrix elements of the type ΔN = ΔF = 0.ΔJ = ± 1. Extra lines obeying the selection rules ΔJ = 0, ± 2 are also induced. Therefore, [sup P]Q₃₄, [sup R]Q₄₃, [sup P]Q₄₃ and [sup R]S₃₄ branches appear in the spectrum although they are not allowed in parallel transitions.
The reason for the great complexity of the spectra is the occurrence of a large avoided crossing near N = 26 in the A⁶Σ + v = 0 level by another electronic state, B⁶Σ +, with the same multiplicity and symmetry. The perturbation between the A⁶Σ + and B⁶Σ + states arises from electrostatic interaction. The selection rules for electrostatic perturbations are ΔJ = ΔS = Δ∧ = ΔΩ = 0. The perturbing state B⁶Σ + state has a considerably longer bond length so that it must come from a "charge transfer transition", possibly by electron transfer either from the 3π to the 4π orbital or from 8σ to 10σ. However, the A⁶Σ + state has only a small bond length change compared to the ground state so that it comes from a "Valence state transition". The Fermi contact constant b was found to be negative for the A⁶Σ + state and this confirms the electronic configuration as being (8σ² 3 π⁴) 1δ² 4 π ² 10σ¹.
The ground state is free of perturbations, except for the internal hyperfine perturbations, and is in nearly pure case (b) coupling. Various satellite branches which were observed in the B-X transition confirm the case (a) nature of the B⁶Σ + state at low N. The spacing between the main branches and the satellite branches gives values for the spin-spin parameter λ and the spin-rotation parameter γ of the ground state. === Science, Faculty of === Chemistry, Department of === Graduate
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