Electronic Absorption Spectrum of Ni II in Cubic Perovskite Fluorides. I

Abstract

The fine structure of the spectrum of Ni²⁺ in KNiF₃ and KMgF₃:Ni has been analyzed in terms of the spin—orbit splitting and vibrational intervals using a four‐parameter crystal‐field approach. The parameters obtained from the analysis differ from the free‐ion values by relatively small amounts, but the differences are not interpretable physically because configuration interaction has been neglected. We find that D_q=698 cm^—1, λ=—(305–320) cm^—1, F₂=1520 cm^—1, F₄=114 cm^—1 (F⁴/F²=0.675). For the free ion we find that λ=—334 cm^—1, F₂=1622 cm^—1, and F₄=116 cm^—1 by fitting the published values for the 3d⁸ energy levels in our analysis with D_q=0. We find that the effects of exchange interaction on the excited state energy levels is small, and that no Jahn—Teller splitting is observed or expected for this crystal. An explanation is offered for temperature changes in the ³A_2g→¹E_g transition involving a breakdown of Born—Oppenheimer separability.