Millimeter-wave spectroscopy of vibrationally excited ground state alkaline-earth hydroxide radicals (X ²Σ⁺)

Pure rotational spectra of the alkaline-earth monohydroxides have been recorded for vibrationally excited states (0 1 0), (0 2 0), (0 3 0), and (1 0 0) of the ground electronic state (X ²Σ⁺) using millimeter-wave absorption spectroscopy. The radicals MgOH, CaOH, SrOH, and BaOH were studied. The data for CaOH, SrOH, and BaOH were analyzed with a linear ²Σ⁺ model, but with the addition of two terms to account for contamination of the υ₂ = 1 ²Π and υ₂ = 2 ²Δ vibronic levels with 2Π and ²Δ electronic states. The data for MgOH, however, did not fit well to this linear model and is additional evidence that this species is quasilinear.