Microwave spectrum of the MnO radical in the X 6Σ+ state

Abstract

The microwave spectrum of MnO in the Σ+6 ground electronic state was detected using a source-modulated submillimeter-wave spectrometer. The MnO radical was efficiently generated by dc sputtering of manganese flakes placed inside a hollow cathode in the presence of an oxygen and helium mixture. In total, 283 spectral lines were measured in the frequency region of 210–450 GHz for nine rotational transitions, each of which showed six fine structure line groups consisting of several hyperfine structure components due to the Mn55 nucleus (I=5/2). A least-squares analysis of the measured line frequencies resulted in the determination of rotational, fine, and hyperfine coupling constants including higher-order spin–orbit distortion terms for the spin–spin, spin–rotation interactions and the Fermi contact interaction of the Mn nucleus. The hyperfine coupling constants were used to assess plausible molecular orbital bonding models.