VIBRATIONAL ANALYSIS OF THE ELECTRONIC ABSORPTION SPECTRUM OF NICKEL (II) IN PEROVSKITE FLUORIDES
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Date
1964
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Ohio State University
Abstract
The absorption spectrum of nickel (II) in $KNiF_{3}$ and $KMgF_{3}:1%Ni$ has been reported $recently.^{1}$ Although an analysis of the spin-orbit structure of the bands was made, a more detailed discussion of the vibrational structure could not be carried out, because the frequencies of the optical phonon modes were not known at that time. Recently, the three $T_{1u}$ fundamental $(k = 0)$ phonon modes of $KNiF_{3}$ have been determined by $Perry^{2}$ so that the structure in the absorption spectrum of $KNiF_{3}$ has been re-examined. These three modes, together with the infrared inactive $T_{2u}$ mode, are observed in the absorption bands which correspond to forbidden electric dipole transitions between the ground state $(^{3}A_{2g})$ and the $^{1}E_{g}, ^{3}T^{a}_{1g}, ^{1}T_{2g}$ and $^{3}T^{b}_{1g}$ states of the nickel (II) ion. The frequencies of the pure electronic spin-orbit states can then be estimated. For the $^{1}E_{g}$ state, a very weak line is observed at its estimated pure electronic energy and this is assigned to the pure electronic transition (magnetic dipole) arising from the spin-orbit mixing between the $^{1}E_{g}$ and $^{3}T_{2g}$ electronic states. A comparison between the observed and calculated spin-orbit mixing between the $^{1}E_{g}$ and $^{1}T_{1g}$ states will be made. Similar absorption spectra taken with crystals of $KMgF_{3}$ containing various concentrations of nickel provide information about the frequencies of localized impurity modes in these crystals. The four degenerate phonon modes are each found to split into three components so that 12 phonon frequencies are observed instead of four in the case of $KNiF_{3}$.
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$^{1}$J. Ferguson, H. J. Guggenheim and D. L. Wood, J. Chem. Phys. 40, 822 (1964). $^{2}$C. H. Perry, personal communication.
Author Institution: Bell Telephone Laboratories, Incorporated
Author Institution: Bell Telephone Laboratories, Incorporated