The microwave spectrum of the methoxy radical CH3O

Abstract

The pure rotational spectrum of the methoxy radical in the ²E ground electronic state was observed in the mm‐wave region using a source‐frequency modulation microwave spectrometer with a 1 m long free space absorption cell. The methoxy radical was produced in the cell by the reaction of methanol with 2450 MHz discharge products of CF₄. Each rotational transition was found to split into fine and hyperfine components. A Hamiltonian was derived which includes the spin‐orbit interaction, the vibronic Coriolis interaction, the (2,−1) and (2,2) rovibronic interactions, and the hyperfine interaction. It was successfully applied to explain the detailed feature of the observed spectrum and to derive molecular constants therefrom. The hyperfine coupling constants of the proton nuclei were determined for the first time. When the C–H bond length was assumed to be 1.0937 Å, the observed A and B rotational constants led to the C–O bond length of 1.376 Å, considerably shorter than the values hitherto accepted.