Studies in Microwave Spectroscopy

Abstract

The theory of microwave spectroscopy is first presented in some detail. Following this, sources of errors in structure determinations based on moment of inertia data are considered, and approximate equations for estimating their effects are derived. A microwave spectroscope has been assembled and its design, construction, and operation are discussed. Microwave spectra in the region from 20 to 25 kmc have been obtained for HN14C12O16, and DN14C12O16. A rotational constant obtained from an infrared study of HNCO by L. H. Jones is combined with the microwave data to yield the interatomic distances and bond angle. High resolution studies of the spectra of HNCO and HNCS permit evaluation of their electric quadrupole coupling constants and qualitative deductions concerning their structures to be made. The molecular species CF3-C≡C-H, CF3-C13≡C-H, CF3-C13≡-H, and CF3-C≡C-D have been observed to absorb in the microwave region, and from the frequencies of these absorptions the C≡C and C-H distances are determined. In addition, the measured moments of inertia are employed to calculate consistent sets of the remaining three parameters in CF3-C≡C-H. The application of the electron diffraction data of W. F. Sheehan, Jr., to this problem to determine which set of parameters actually represents the structure is described. Stark effect measurements are presented which determine the dipole moments of HN14C12O16 in three vibrational states and of DNCO, OCS, H2CO, CHF3, and CHF3-C≡C-H in their ground states. Finally, attempts to obtain microwave spectra for several other compounds are briefly described.