Hyperfine Structure inO17H and the OH Dipole Moment

A microwave spectrometer for the study of free radicals or other reactive species is described; it can be used with either Stark or Zeeman modulation. This spectrometer was used to determine the hyperfine structure of ${\mathrm{O}}^{17}$H. Four main lines of the ${}_{}{}^2{}_{}{}^{}\pi _{\frac{3}{2}}^{}{}_{}{}^{}$, $J=\frac{7}{2}$ $\Lambda$-doubling transition were definitely observed, and there is evidence that one satellite line was also detected. Quantum number assignments were made for the four main lines, which are divided into two doublets. In the course of establishing the uniqueness of these assignments, the $\Lambda$-doubling frequency for the ${}_{}{}^2{}_{}{}^{}\pi _{\frac{3}{2}}^{}{}_{}{}^{}$, $J=\frac{7}{2}$ state of ${\mathrm{O}}^{18}$H was experimentally determined. The separation between doublets in the ${\mathrm{O}}^{17}$H spectrum was used to determine the hyperfine constant $d$ associated with the ${\mathrm{O}}^{17}$ nucleus. The constant $d$ was also computed theoretically from a simple molecular model of OH in which a single unpaired $p\pi$ electron about the ${\mathrm{O}}^{17}$ nucleus is assumed. The experimental value is about 8% greater in magnitude than the theoretical value, and this difference is discussed. The same spectrometer was used for the determination of the electric dipole moment of OH by measuring the Stark shift of the ${}_{}{}^2{}_{}{}^{}\pi _{\frac{3}{2}}^{}{}_{}{}^{}$, $J=\frac{7}{2}$, $M=4\mathrm{}$ $\Lambda$-doubling line of ${\mathrm{O}}^{16}$H at a known electric field. The OH dipole moment was found to be 1.60±0.12 D.