Assignment of the lowest 3Π and 1Π states of CaO, SrO, and BaO

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Abstract
New techniques for the assignment of perturbations in electronic spectra are described and applied to perturbations in the A1Σ-X1Σ bands of CaO, SrO, and BaO. These techniques utilize observed perturbation matrix elements to establish electronic and vibrational assignments of perturbing states. Using only data reported by Lagerqvist and co-workers between 1949 and 1951 it has been possible to assign perturbations of the A1Σ+ state to a 1Π state (A′1Π) and to three components of an inverted 3Π state (a3Πi). Absolute vibrational assignments have been made and the following spectroscopic constants obtained (in cm−1 with one standard deviation uncertainty in the last digit in parentheses): CaOSrOBaOA′1Πa3ΠiA′1Πa3ΠiA′1Πa3Πiν008564(16)8225(25)9794(10)9055(5)17 568(10)17 372(10)A (3Π)⋯−58(3)⋯−70(2)⋯−105(10)ωe557.5(86)556.2(100)460.3(8)463.5(8)448.3(7)448.3(7)ωexe3.31(20)3.30(22)1.61(5)1.61(5)2.39(13)2.39(13)Be0.3353(68)0.3353(68)0.2610(5)0.2584(5)0.2244(5)0.2244(5)αe0.0015(7)0.0015(7)0.0023(4)0.0020(2)0.0014(2)0.0014(2)The A′1Π-a3Π energy separations are small, and the a3Π state, the lowest state which dissociates to ground state atoms, lies at surprisingly high energy. The X1Σ+ state is now proven to be the ground state of BeO, MgO, CaO, SrO, and BaO.