The microwave spectrum of the LiO radical

The rotational spectra of the 7LiO radical in the v=0 and v=1 vibrational states were observed in the millimeter and submillimeter wave region. The LiO radical was generated by the reaction of lithium vapor with N2O directly in a high temperature absorption cell. The rotational and centrifugal distortion constants, Λ-type doubling constants, spin–orbit interaction constant, and hyperfine interaction constants were derived through analysis of the rotational spectra observed in the present study combined with the radio frequency spectra of Λ-type transitions reported by S. M. Freund et al. [J. Chem. Phys. 56, 1467 (1972)]. The LiO radical was confirmed to have a 2Πi ground electronic state with an exceptionally large Λ-type doubling constant, as in the case of NaO. A pure precession hypothesis applied to the observed p Λ-type doubling constant gives the Σ–Π energy difference to be 2565 cm−1.