High-resolution laser excitation spectroscopy of the A∼2Π(000)-X∼2Σ+(000) transition of BaOH

The high-resolution spectrum of the A∼2Π(000)-X∼2Σ+(000) transition of BaOH has been recorded using laser excitation spectroscopy. The BaOH molecules were synthesized through the reaction of Ba atoms with H2O2 in a Broida-type oven. Rotational and fine structure parameters have been determined for the A∼2Π(000) state through a combined least-squares fit with the millimeter-wave pure rotational data of the X∼2Σ+ state. The Λ-doubling constants observed for the A∼2Π state are in poor agreement with the predictions of the pure precession model of the interactions between the A∼2Π and the B∼2Σ+ states of BaOH. In addition to the bands of the A∼2Π(000)-X∼2Σ+(000) transition, three bands located at ∼11 443 cm−1, ∼12 013 cm−1 and ∼12 505 cm−1, respectively, were also observed and analyzed but their vibrational and electronic assignments are not clear. Possible assignments of the three unidentified bands are discussed based on the derived spectroscopic constants and the vibrational assignments of previous low-resolution work.