NUCLEAR RADIO-FREQUENCY SPECTRA OF A SERIES OF TETRAHEDRAL MOLECULES

The molecular-beam magnetic-resonance method has been applied to a series of tetrahedral molecules. In each case, the radio-frequency spectrum was observed which corresponds to the reorientation of the total nuclear spin with respect to a large external magnetic field. In order to analyze these spectra, the energy levels of the complete spinrotation interaction and the direct dipole-dipole interaction have been calculated to first order in high-field perturbation theory by applying the recent group-theoretical treatment of Yi, Ozier, and Anderson. On the basis of these energy levels, the theoretical spectrum for each molecule has been constructed on a high-speed digital computer. By fitting this theoretical spectrum to the data, it has been found that: for CH4 ca=(10.4±0.4) kHz cd=(21±8) kHz SiH4 (3.88±0.23) (9.0±3.5) GeH4 (3.62±0.20) (5.5±5.0) CF4 (6.85±0.35) -13≤cd≤17 SiF4 (2.42±0.08) |cd|≤3 GeF4 (1.88±0.08) |cd|≤3, where ca is the average spin-rotation constant and cd is the anisotropy in the spin-rotation matrix. Only the relative sign of these two constants was determined. Several earlier approximate methods of treating spherical rotor problems which involve the tensor part of the spin-rotation interaction are examined in the light of the present results. © 1968 The American Physical Society.