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 where $c_a$ is the average spin-rotation constant and $c_d$ 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.