Beam maser measurements of HDO hyperfine structure

The 431←432, 532←533, and 321←414 transition in HDO were measured in a beam maser spectrometer. Accurate values for rotational transiton frequencies, the deuterium quadrupole coupling tensor, and hydrogen spin‐rotation tensor were obtained from the present data combined with previous results on other transitions. Resonance line widths of 2 kHz were obtained for most of the data. Measured quadrupole coupling tensor elements eqQ(D)gg and spin‐rotation tensor elements C(X)gg in kHz are as follows: eqQ(D)aa = 276.45±0.88, eqQ(D)bb = −110.97±1.46, eqQ(D)cc = −165.77±1.10, C(D)aa = −1.33±0.20, C(D)bb = −4.38±0.36, C(D)cc = −2.99±0.24, C(H)aa = −58.42±0.47, C(H)bb = −5.46±0.83, C(H)cc = −24.11±0.55.