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Title: The optical properties of caesium pentachloromanganate (II)
Author: Tacon, R. John
ISNI:       0000 0001 3495 4513
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1977
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Absorption spectra of tetragonal single crystals of Cs3MnCl5 have been measured at 4.2K over the wavelength range 5200-2600Å. Spin forbidden bands of low oscillator strengths were observed for the 4Γ ← 6A1 transitions of the MnCl42- chromophore. All the intensity arose from the electric dipole mechanism, but for small magnetic dipole contributions to the intensities of 4E(G) and 4T2(F). Magnetic circular dichroism spectra measured at 4.2K in a field of 4.75 Teslas were dominated by C-term signals. The band intensities were assumed to arise via the spin orbit interaction, allowing "intensity borrowing" from higher energy charge transfer transitions. A model based on tetrahedral symmetry for the chromophore ion allowed the calculation of MCD:absorption intensity ratios for the quartet states. Good agreement was found with the experimental values for most quartets. Crystal Field calculations were performed in support of the MCD-based band assignments. Covalency was introduced into Stout's electrostatic matrices via the Koide and Pryce parameter andepsilon;. The following parameter values were found: B = 600cm-1 , C = 2940cm-1, Dq = 350cm-1, and ε = 0.03, giving the correct ordering of the states and an rms. deviation from the observed energies of 520cm-1. 4A2(F) was placed above 4T1(F) in energy, a departure from the "conventional" 4F term assignment. A simplified model for the perturbation of the cubic states by the tetragonal component of the crystal field was developed to account for the observed linear polarisations. The spectra were examined in detail to identify the electronic origins and assign them using a tetrahedral or tetragonal scheme. The latter appeared to be the more realistic model for most states. Assisted by data from the Raman spectrum, the vibrational sidebands were also assigned, When very sharp origin lines were present, some of the sidebands showed small splittings attributable to the presence of the two chlorine isotopes.
Supervisor: Denning, R. G. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available