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 N¹⁴{H}₃$ and the 1-1, 2-2, and 3-3 transitions in ${N}¹⁵H₃ has been measured with a two-cavity maser spectrometer. This device employs Ramsey's method of separated oscillating fields to obtain a molecular resonance linewidth of 350 cps. The theory of Gunther-Mohr et al. and of Gordon has been extended to include all terms off-diagonal in F₁≡IN+J in an attempt to explain some discrepancies between the previous theory and our measurements. The interactions included in this treatment are the nitrogen quadrupole interaction, the nitrogen IN·J interaction, the hydrogen I ·{} J interaction, the hydrogen-nitrogen spin-spin interaction, and the hydrogen-hydrogen spin-spin interaction. The strengths of these interactions are treated as adjustable parameters in least-squares fit programs which determine the parameters by fitting the experimental data. There are still significant deviations between theory and experiment for the 1-1, 3-3, and 3-2 transitions of N¹⁴{H}₃$ and for the 1-1, 2-2, and 3-3 transitions of ${N}¹⁵H₃. The largest discrepancies occur for the N¹⁴{H}₃$ 3-2 transition and the 1-1, 2-2, and 3-3 transitions in ${N}¹⁵H₃ where the quadrupole interaction vanishes. The discrepancies are greater than 1 kHz in these cases. According to the theory, pairs of satellites of the N¹⁵{H}₃$ 2-2 transition should occur at the same frequency, and these are all split by 4 kHz. In addition, the values of the ${N}¹⁵H₃ coupling parameters do not agree with theory.