LASER VAPORIZATION-FOURIER TRANSFORM MICROWAVE STUDY OF THE HYPERFINE STRUCTURE OF THE $J = 3/2 \leftarrow 1/2$ ROTATIONAL TRANSITION OF $X^{4}\Sigma^{-} Nb0$.

$^{1}$ G. Cheval, J. L. Femenias, A. J. Merer and U. Sassenberg, J. Mol. Spectrosc. 131, 113-126 (1988).Author Institution: Department of Chemistry, Rensselaer Polytechnic Institute; Molecular Physics Division, National Institute of Standards and TechnologyThe NbO radical has a $^{4}\Sigma^{-}$ ground electronic state. The $^{3}Nb$ nucleus has a spin of 9/2 and one of the largest nuclear magnetic moments of any nuclei. All of these factors contribute to make the optical spectrum of NbO extremely complex with large hyperfine effects being observed. Based on results from previous high resolution optical $studies^{1}$. several hyperfine components of the $J=3/2 \leftarrow 1/2$ rotational transition were predicted to fall in the 6-26 GHz frequency range of our pulsed Fourier transfor microwave spectrometer which is equipped with a laser vaporization source. Spectral searches have led to the observation of four of the five observable hyperfine components of this transition in the $v=0$ state as well as several satellite transitions that are believed to arise from the $v=1$ state. From a Stark analysis of two of the hyperfine components a dipole moment of -3.2D has been determined