Low-Field Hyperfine Spectrum of CH4

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Abstract
The hyperfinespectrum of CH4 has been observed in the low field limit by the molecular‐beam magnetic‐resonance method. Ten partially resolved lines were observed in the frequency region below 100 kHz. The lines associated with the nuclear quintet were found to be equally spaced with frequencies which depend only on the average spin‐rotation constant ca . The lines associated with the nuclear triplet were found to form a complex spectrum with frequencies which depend not only on ca , but also on the anisotropy in the spin rotation matrix cd and on the tensor spin—spin coupling constant d. In the analysis of the triplet spectrum, the energies of the tensor interactions have been calculated in detail by applying the recent group theoretical treatment of Yi, Ozier, and Anderson. It was determined that c a = + (10.4 ± 0.1) kHz ; c d = + (18.5 ± 0.5) kHz and d = + (20.9 ± 0.3) kHz . For these values, the calculated and experimental frequencies agree to within a rms deviation of 350 Hz.