Measurement of ammonia hyperfine structure with a two-cavity maser

Hyperfine structure of the J-K=1-1,2-2,3-3, and 3-2 inversion transitions in N14H3 and the 1-1, 2-2, and 3-3 transitions in N15H3 has been measured with a two-cavity maser spectrometer. This device employs Ramsey's method of separated oscillating fields to obtain a molecular resonance linewidth of 350 cps. The theory of Gunther-Mohr et al. and of Gordon has been extended to include all terms off-diagonal in F1IN+J in an attempt to explain some discrepancies between the previous theory and our measurements. The interactions included in this treatment are the nitrogen quadrupole interaction, the nitrogen IN•J interaction, the hydrogen I • J interaction, the hydrogen-nitrogen spin-spin interaction, and the hydrogen-hydrogen spin-spin interaction. The strengths of these interactions are treated as adjustable parameters in least-squares fit programs which determine the parameters by fitting the experimental data. There are still significant deviations between theory and experiment for the 1-1, 3-3, and 3-2 transitions of N14H3 and for the 1-1, 2-2, and 3-3 transitions of N15H3. The largest discrepancies occur for the N14H3 3-2 transition and the 1-1, 2-2, and 3-3 transitions in N15H3 where the quadrupole interaction vanishes. The discrepancies are greater than 1 kHz in these cases. According to the theory, pairs of satellites of the N15H3 2-2 transition should occur at the same frequency, and these are all split by 4 kHz. In addition, the values of the N15H3 coupling parameters do not agree with theory.