Microwave spectrum of the NiO radical in the X(3)Sigma(-) state

The microwave spectrum of NiO in the (3) Sigma(-) electronic ground state has been observed using a source-modulated millimeter and submillimeter wave spectrometer. NiO was generated by de-sputtering vaporization of powdered NiO. Rotational transitions of (NiO)-Ni-58 and (NiO)-Ni-60 in the vibronic ground state were measured in the 110-460 GHz region and those of (NiO)-Ni-58 in the upsilon = 1 state in the 240-370 GHz region. Precise molecular constants were obtained by a least-squares analysis of the measured frequencies. The r(e) bond length is obtained to be 1.6271291(31) Angstrom with three standard errors in parentheses.