Microwave Spectrum of the SO Radical

Five microwave transitions of the SO free radical in the gas phase have been measured and assigned. The lines result from electric dipole transitions between rotational levels in the 3Σ— ground state which are strongly perturbed by the interaction of the electron spin. The molecular constants determined from the analysis are B0=0.71791 cm—1, λ=5.276 cm—1, and γ=—0.0052 cm—1. The electric dipole moment has been determined as 1.55 D from the Stark effect. Wavefunctions and intensities are discussed. A combination of microwave and optical data gives Be=0.72072 cm—1 and re=1.48095 Å for the ground state and λ=3.5 cm—1 for the excited B 3Σ— electronic state. The spectrum was studied in a flow system in which SO was generated by the reaction of oxygen atoms with OCS or other materials. The apparatus is described in detail.