The hyperfine and Zeeman components of the 3–2–22 and 43–51 transitions of D2O, the 22−21 transition of HDO, and the 6−5−5−1 transition of H2O have been measured with a beam-maser Zeeman spectrometer. This allowed determination of the elements of the magnetic moment tensor Ggg and of the anisotropic part of the magnetic susceptibility tensor (χgg–χAv) for D2O. The best fit results are (for χgg–χAv in 10−8kHZ G−2): Gaa = 0.32530(10), Gbb = 0.36009(22), Gcc = 0.32513(15), χaa–χAv = 3.88(20), χbb–χAv = − 1.66(40), χcc–χAv = − 2.23(30). From these values the elements of the molecular quadrupole moment tensor for D2O have been determined (in 10−26 esu·cm): θaa = 2.72(2), θbb = − 0.32(3), θcc = −2.40(2). The sign of the molecular electric dipole moment and the validity of the isotopic invariance of the electronic charge distribution have been investigated by comparing the molecular magnetic moments of D2O, HDO, and H2O. The obtained experimental values for several one-electron properties are in fair agreement with recent accurate ab initio calculations.

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The molecular beam electric resonance method was employed to obtain a complete set of hyperfine Λ doubling transitions of the free radicals OH, OD, SH, and SD. The observed spectra could be explained very well by the degenerate perturbation theory adapted to the 2Π state. The experimental results include fine and hyperfine coupling constants, the electric dipole moments could be explained very well by the degenerate perturbation theory adapted to the 2Π state. The constants agree well with ab initio calculations.

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Hyperfine structure of the 22→21 rotational transition of HD17O at 10.374 GHz has been investigated with a beam-maser spectrometer. The best-fit results for the spin–rotation coupling constants CJτ(K) and for the components χij(K) of the quadrupole coupling tensors in their principal coordinate systems are in kHz: C22(H) = − 42.20 ± 0.20; C21(H) = − 42.98 ± 0.20; C22(D) = − 2.04 ± 0.02; C21(D) = − 2.0000 ± 0.0015; C22(O) = − 22.5 ± 0.3; C21(O) = − 22.35 ± 0.20; χxx(O) = 10 175 ± 67; χyy(O) = − 8 891 ± 21; χzz(O) = − 1283 ± 87; χx′x′(D) = 307.90 ± 0.14; χz′z′(D) = − 133.13 ± 0.14; χy′y′(D) = − 174.78 ± 0.29; η(O) = (χzz(O) − χyy(O)) / χxx(O) = 0.75 ± 0.01. These results show good agreement with recent ab initio calculations and remove the discrepancy with the experimental results of Stevenson and Townes (η(O) = 1.83 ± 0.20).

The spectrum of gaseous KCN was measured in the frequency range between 2 and 39 GHz by microwave absorption and by molecular-beam electric-resonance spectroscopy. Combination of the new results with earlier microwave data of KCN in the 100 GHz range made it possible to assign 64 transitions to the ground vibrational state and to fit them to the asymmetric rotor model. The three rotational constants, the five quartic distortion constants, and two sextic distortion coefficients could be determined. Assuming a CN distance of 1.162(10) Å we find rKC=2.6(1) Å and uKCN=76 °(10). The molecules thus have a nonlinear, T-shaped structure. The inertial defect gives an estimated value of the lowest vibrational frequency of KCN ω2=157 cm−1, which is in reasonable agreement with ω2=139 cm−1 from matrix-isolation studies.