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Magnetic circularly polarized emission (M.C.P.E.) and magnetic circular dichroism (M.C.D.) techniques have been used to study at low temperatures resolved vibronic lines of the ~A,g~-*2Eg transition in octahedral Mn4+(3d 3) in the cubic host C%GeF6. Measurements have been made with applied magnetic field (and light propagation) along the [001 ] (F-Mn-F bond) and[111] directions. Though the Zeeman energy patterns are isotropic, the intensity patterns are not, and U'(Fa) eigenvectors for arbitrary field orientation have been derived. These have been used to calculate Zeeman intensity patterns for the [001 ] and [111 ] crystallographic directions, and the observed intensity variations with orientation are found to provide useful information about intensity mechanisms. In the case of the magnetic dipole origin, the intensity patterns as a function of orientation can be well accounted for by a first-order mechanism which, however, does not predict the small positive M.C.D. observed at the zero-field energy in the [111] orientation. A detailed analysis of this feature and previously measured energy spacings suggest that gaa(Mn 4+) should have a value of ~ 360 cm -1 rather than the value 240 cm -1 usually assumed. Electric dipole vibronic sidebands have been observed corresponding to vo(t~u), vr v3(tlu), v4(tlu) + vs(t2a) and v~(eg) + v6(tau). Using a U' ~U' vibronic intensity mechanism with spinorbit mixing (Appendix A), the M.C.P.E. and total emission patterns for the first two of these regions can be quite well accounted for quantitatively. The corresponding M.C.D. in both cases, while in qualitative agreement with the M.C.P.E., shows much more complicated splitting patterns which are not explicable in terms of a simple k=0 model. The other three vibronic regions can be accounted for qualitatively. In Appendix B a formula is derived which explicitly relates the M.C.P.E. of a vibronic emission line to its M.C.D. absorption counterpart.

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The Eg″ (2T2g)→ Eu″(2T2u)+Uu′(2T2u) allowed ligand-to-metal charge-transfer bands in octahedral ral IrCl62−(Cs2ZrCl6:Ir4+) which correspond to the excitation t2u(π)→t2g(d) show a highly resolved complex vibronic pattern over the region 22 900 – 24 500 cm−1 at liquid helium temperature. In this paper, it is shown that this spectrum can be interpreted in detail on the basis of a strong Jahn-Teller effect in the t2g molecular mode. The treatment is carried out in a basis spanning all vibronic functions through the first 11 quanta of the undisplaced t2g harmonic oscillator functions. All matrix elements involving both the first order Jahn-Teller Hamiltonian and spin-orbit coupling are included in a complete diagonalization. A large Ham effect quenches the spin-orbit coupling so that the no-phonon lines of the two spin-orbit components (Eu″ and U′u) are separated by ∼5–6 cm−1 rather than the expected value of ∼(3/4)ζCl≈440 cm−1. The calculated results explain semiquantitatively the over-all band spectrum in both absorption and MCD as well as the behavior of the no-phonon lines as a function of magnetic field (up to ∼70 kG) and temperature. There is additional low energy vibrational structure, undoubtedly due to lattice vibrations, the most important of which is probably Jahn-Teller active. The eg molecular vibration appears weakly, if at all. An alternative treatment assuming a strong Jahn-Teller effect in the eg mode does not satisfactorily account for the observed spectrum. Arguments are suggested to account for t2g rather than eg Jahn-Teller activity.

Liquid helium temperature magnetic circular dichroism (MCD) data are presented and analyzed in some detail for the 4A 1, 4E region of MnF2 and K2MnF4 with attention focused on the magnetic dipole origins. The MCD technique is ideal in this regard since it shows very prominent pseudo-A terms for the π-polarized origins while effectively ``filtering out'' almost all of the much more intense electric dipole absorption. In this experiment, the 4A 1 origin of MnF2 has been directly observed for the first time about 143 cm−1 to the blue of the 4Eθ origin, as predicted. The signs of the A terms provide an independent confirmation of the accepted order of the two states. The observed magnitudes of the MCD and absorption parameters can be rationalized on the basis of a simple octahedral model if substantial mixing (85%/15%) of the 4E θ and 4A 1 states is assumed. In K2MnF4 two very sharp ([inverted lazy s]1 cm−1) magnetic dipole origins are observed in the π and axial spectrum separated by 25.1 cm−1 which show very prominent A terms of opposite sign. Theoretical analysis of the MCD shows that the higher energy of these must correspond to the 4E ε origin. The lower energy origin is assigned to 4E θ, and a prominent A term about 350 cm−1 to the blue can be assigned with reasonable confidence to the 4A 1 origin, which is not evident in the absorption spectrum. The A terms that have been assigned to the three origins vanish above the spin-flop field as expected. The absorption and MCD parameters for 4E ε are substantially smaller relative to 4E θ and 4A 1 than is predicted on the basis of a simple octahedral model.