The ground state of KO revisited: the millimeter and submillimeter spectrum of potassium oxide

Abstract

The millimeter/sub-millimeter spectrum of the KO radical has been recorded in the frequency range 90–534 GHz using direct absorption methods. The radical was synthesized by reacting potassium vapor, produced with a Broida-type oven, with either N₂O or O₂ mixed in argon carrier gas. Twenty-seven rotational transitions of KO were measured, each exhibiting a doublet structure with a relatively small splitting (∼100–200 MHz) that increased noticeably with frequency. A perturbation was apparent in the rotational lines at energies above ∼120 cm⁻¹, which was more prominent in one doublet component. The data were successfully fit with a Hund's case (c) Hamiltonian, assuming that spectra arise from a ²Π_i state, and rotational and effective lambda-doubling constants were determined. Higher order centrifugal distortion terms were needed to account for the perturbation. The spectra could also be fit as a ²Σ⁺ ground state, but less successfully, and the resulting rotational constant of B = 8235.4 MHz disagreed significantly with that predicted by theory. On the basis of the experimental data, the ground electronic state of KO has been assigned as ²Π_i, although the ²Σ⁺ assignment cannot be entirely ruled out.