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The electron spin resonance spectrum of the vanadyl ion (VOH) in single crystals of Zn (NH4h (S04h• ?H20 is studied and the properties of x-ray produced V2+ arc compared to those of the V2+ grown directly mto the same host lattice. In the un irradiated samples the V-O axis is found to have three possible orientations with populations in the ratio 20: 5: 1. For the most populous position the spin Hamiltonian parameters at X band are S=t gx=1.9813, gy=1.9801, g.=1.9331, A x =0.007120/cm, A y=0.OO7244/cm, A.= 0.018281/cm, and Q' = 7X 1O-5 /cm with the x, y principal axes of the g and A tensor being displaced from each other by 23°20'. Furthermore, the vanadyl hyperfine lines show an additional anisotropic structure of five lines, absent in deuterated samples. The parameters for V2+ at K band in both the as-grown and irradiated crystals are S=3/2, g.= 1.9717, gy= 1.9733, D= -0.15613/cm, E= -0.02280/cm, and A = -0.00825/cm. A study of the effect of x-ray dose upon the line intensity is made. An impurity model of a vanadyl pentahydrate complex associated with a water moleculy vacancy is proposed.

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Single crystals of CdF2 containing either V3+ or V2+ ions have been prepared and studied by optical, EPR, and ENDOR techniques. As expected, the properties of V3+ in the eight-coordinated (cubal) environment closely resemble those of Ni2+ in octahedral sites. The ENDOR data show that Ms = ± 1, confirming the identification of the ion as V3+. The V2+ ions, produced by heating samples containing V3+ in Cd vapor, exhibit evidence for a large trigonal Jahn–Teller distortion of the cubal site. On the basis of the EPR and optical data it is suggested that the environment about the V2+ ions may be more nearly octahedral than cubal, thus reflecting the presence of a static trigonal field comparable in magnitude to the (undistorted) cubic field. Some optical and EPR data are presented for isoelectronic Cr3+ ions, which also display a strong Jahn–Teller effect.

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