The electron paramagnetic resonance of Gd3+ has been studied in a single crystal of thorium oxysulfide. The experimental results are interpreted using a spin Hamiltonian for tetragonal symmetry, and the crystal-field parameters and the g factor are determined. The very good agreement between the calculated and experimental data shows that the Gd + ion enters substitutionally, and that the charge compensation is far enough away to avoid any distortion of the local symmetry.

The spin Hamiltonian parameters of Gd 3+ in a single crystal of Thorium disulfide (TI1S2) are analysed by means of the superposition model, in its most general form of a two exponents power law. In fact, the approximated one exponent power law is not suitable for this compound, where the ion-ligand distances show a quite large spread. The results of the analysis are then applied to the case of Gd 3+ doped Thorium oxysulfide (ThOS), where the fitting of the experimental data is possible only assuming some distortion of the ligand cage.

Some chlorosubstituted cupric acetates are studied by E P R (X-band) in order t o examine the effect of different environments on the exchange interactions between the cupric ions. I n hydrated and anhydrous tri-and dichlorosubstituted cupric acetates only isolated ions are present, while hydrated cupric acetate and monochloroacetate show only exchange-coupled ion pairs. However, in anhydrous cupric acetate and monochloroacetate both these situations are found to occur. Some possible interpretations of these results are given.Nous avons etudie par la r.p.e. (bande X) quelques acetates de cuivre chlorosub stitues pour examiner l'influence du different entourage sur les interactions d'echange entre les ions cuivriques. Dans les acetates de cuivre tri-et dichlorosubstitues, hydrates et anhydres, on trouve seulement des ions isolks, et dans l'acetate e t le monochloroacetate hydrates seulement des paires d'ions couples par Bchange. Dans l'acetate et le monochloroacetate anhydres nous avons observe tous les deux situations et nous donnons des possibles interprktations.

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