Faraday Effect of Charge-Transfer Transitions in Fe(CN)63−, MnO4−, and CrO42−

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Abstract
Measurements of the magneto‐optical rotatory dispersion (MORD) and magnetic circular dichroism (MCD) through the accessible charge‐transfer bands of Fe(CN)63−, MnO4−, and CrO42− in the visible and ultraviolet are described and interpreted. The apparatus employed combines a superconducting solenoid furnishing maximum fields of 45 000 G with a commercial ORD—CD instrument which covers the range 185–700 mμ. The MCD measurements are found to be more reliable and are much easier to make; they are also more useful for theoretical interpretation. However, Kramers—Kronig transforms of the MORD results agree well with the experimental MCD measurements. Comparison of the theoretically derived Faraday parameters for Fe(CN)63− with those extracted from experiment shows that the 24 000‐, 33 000‐, and 38 500‐cm−1 bands are due, respectively, to 2T2g→2T1u, 2T2u and 2T1u, ligand‐to‐metal(t2g) charge‐transfer transitions. A similar analysis confirms the assignment of the lowest band in MnO4− and CrO42− to a t1(π)→e(π) transition. The observed parameters for higher bands agree well with predictions based on the recent Wolfsberg—Helmholz calculation of Viste and Gray but do not unambiguously confirm their assignments.