Interpretation of the Absorption Spectra of K3Fe(CN)6

Abstract

By interpreting the absorption spectra of K₃Fe(CN)₆ in solution, we are able to explain the results of the pressure dependence of the solid spectra, obtained by Parsons and Drickamer. The intense absorptions at 24 000 and 32 900 cm^—1, are identified as charge‐transfer spectra from the ligand to the T_2g level of the metal ion, while the one at 38 460 cm^—1 is identified as the same type of transition, but into the E_g level. Fitting of the weaker spectra yields the values of 3500, 720, and 3285 cm^—1 for the crystalline field parameters D_q, B, and C, respectively. One of the results of Parsons and Drickamer shows evidence of a charge‐transfer transition that is symmetry restricted, and made allowed by vibrational‐electronic perturbations. A perturbation treatment is carried out that follows the method developed by Liehr and Ballhausen for the dⁿ→dⁿ crystal‐field transitions, that are also symmetry forbidden. Finally, two types of experiments that would test the proposed explanations are described.