A molecular-beam-optical and radio frequency-optical double-resonance study of the a ²Π_r-X²Σ⁺ band system of scandium monoxide

A molecular-beam-optical and rf-optical double-resonance study of the A ²Π (v′ = 0-2) -X²Σ⁺ (v″ = 0-2) band systems of gas phase scandium monoxide has been performed. No localized perturbations in the X²Σ⁺ state have been observed but strong perturbations in the A ²Π_r (v = 1) state were detected. Quantum numbers for the optical spectrum could only be assigned assuming a negative value for the excited state Λ-doubling-type magnetic hyperfine parameter, contrary to current theoretical understanding of this interaction. The ground state magnetic hyperfine parameters can be interpreted in terms of ab initio models for the electronic states of ScO whereas the spin-rotation parameters cannot.