Magnetic circular and linear dichroism of cubic or tetragonally distorted high spin d5systems

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Abstract
The low temperature, single crystal and polymer matrix absorption, magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) of the d-d electronic transitions in the tetrahalomanganates (II), [(C2H5)4N]2MnX4 (where X = Cl, Br and I), have been investigated. The effect of crystal rotation about the incident radiation propagation direction is theoretically examined and shown to yield anisotropic MLD terms for 4 T 1 and 4 E states and isotropic ones for 4 A 2 and 4 T 2 states. The combination of the sign of the MCD zeroth order moment and the MLD crystal rotational dependence is used to assign the observed bands with a high degree of certainty. It is shown that although conventional crystal field theory correctly predicts the d-d state ordering in the lowest energy range (4 T 1 < 4 T 2 < 4 E) it fails badly in the higher energy region (4 T 1 < 4 T 2 < 4 A 2). An improved model including both charge-transfer and d electron configurations is proposed to explain the discrepancy. Spin-orbit and tetragonal field calculations are shown to play a very effective role in explaining fine details in our experimental spectra. Finally, evidence for Jahn-Teller activity in several bands is noted.