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An electron paramagnetic resonance study of a manganese (IV) ion in a trigonal environment Byfleet, Colin Russell

Abstract

An electron spin resonance study has been carried out at room temperature, on a magnetically dilute single crystal of ammonium 9-molybdomanganate. A general method for fitting E.S.R. results to a spin Hamiltonian has been devised, and the results of the above study have been used as an example of this method. The values of the parameters thus determined were⃒D⃒= 0.861 ± 0.001 cm⁻¹; g〟 = 1.9920 ± 0.0004 cm⁻¹; g⊥± = 1.9880 ± 0.0004 cm⁻¹;⃒A〟⃒= 0.00760 ± 0.00004 cm⁻¹;⃒A⊥⃒= 0.00684 ± 0.00004 cm⁻¹1. A review of previous theoretical calculations on d³ has been given, and a ligand field approach has been taken in an attempt to interpret the observed parameters. This was successful for the zero field splitting and hyperfine coupling constants, but not for the g-values. The experimental results from a study of an irradiated, single crystal of deuterated ammonium paramolybdate tetrahydrate have also been fitted to a suitable spin Hamiltonian. The principal axes of the g and A tensors were found not to be coincident, and a method for treating the experimental results in this situation has been given. This study showed that the doublet splitting observed earlier, in the E.S.R. spectrum of the irradiated, undeuterated compound, was most probably due to a captured proton. An interpretation of the observed g-values and hyperfine coupling constants has been given, using a molecular orbital approach.

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