The magnetic resonance spectra of the ground 2P multiplets of 11B and 27Al have been remeasured by the method of atomic beams and the coupling constants A3/2, B3/2, and gJ(2P3/2) and gJ(2P1/2) for 11B, and A1/2 for 27Al, have been redetermined to higher precision. Measurements have also been made, by the triple resonance method, of two ΔMJ = 0, ΔMI = ± 1 transitions in both 11B and27 Al and from these the off-diagonal magnetic dipole coupling constants A3/2,1/2 have been determined.These measurements have enabled us to evaluate the magnetic dipole radial parameters [Formula: see text], [Formula: see text], and [Formula: see text] for both boron and aluminum. The departures of [Formula: see text] and the ratio [Formula: see text] from their restricted Hartree–Fock values are plotted as functions of the occupation number N for all elements with (2p)N and (3p)N ground configuration for which data are available. The trends are briefly discussed.

The spin-Hamiltonian parameters for Gd3+ in CaWO4 have been measured by the method of electron spin resonance at a number of temperatures between 4.2 °K and 300 °K. The results at 78 °K are in agreement with previous measurements by Hempstead and Bowers.The variations in the crystal-field parameters are interpreted in terms of a limiting low temperature value and a normalized slope at the Debye temperature for each parameter. These quantities are compared with the corresponding quantities for Eu2+ in CaWO4 and, in the case of the fourth-order parameters, for Eu2+ and Gd3+ in cubic CaF2, SrF2, and BaF2. We conclude that the second- and fourth-order splittings each arise from at least three competing mechanisms and that these include a dependence on the amplitude of lattice vibrations. In the case of the trivalent ion, Coulomb forces are also considered to be important.

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The EPR spectrum of O2 impurity in solid N2 has been observed at K band and at X band. The results are consistent with the specific-heat results for this system and indicate that the Σ3 state is split in zero field by 105 ± 15 GHz. A small temperature-dependent splitting of the upper doublet is indicated by the results, and the possibility of using O2 as a probe to investigate the motions of molecular solids is pointed out.

The hyperfine structure coupling constants of the ground 3 P multiplet of 17 O have been measured in a paramagnetic resonance experiment with a sample of enriched oxygen gas. They are: a 2 = – 218.569 ± 0.004 Mc/s, a 1 = 4.738 ± 0.036 Mc/s, a 2,1 = –126.6 ± 2.0 Mc/s, a 1,0 = – 91.7 ± 7.2 Mc/s, b 2 = –10.438 ± 0.030 Mc/s, b 1 = 5.199 ± 0.090 Mc/s. These results confirm the values of a 2 and b 2 reported previously by Kamper, Lea & Lustig 1957. Measurements have also been made on the excited level of the ground 2 P multiplet of 19 F. They yield: a ½ = 10244.21 ± 0.03 Mc/s, g J ( J = ½) = 0.66561 ± 0.00003. An analysis of the magnetic hyperfine constants in the ground multiplets of 17 O and 19 F shows that in neither case do they yield consistent values for the two parameters < r -3 > and | ψ (0)| 2 usually associated with magnetic hyperfine structure. All measurements of hyperfine structure in these multiplets are consistent, however, with the requirements of LS coupling theory which introduce a third parameter into the magnetic hyperfine operator. The discrepancy is attributed to polarization effects, other than spin polarization of the core s electrons, brought about by the exchange interaction between electrons.