Study of the Initial Tetragonal Distortion of the [CoX4]2- Complex-Ion (X=Cl or Br) in Cs3CoCl5 and Cs3CoBr5 Crystals by the Effect of Uniaxial Stress on Optical Absorption-Lines. II. Analysis and Estimation of the Jahn-Teller Coupling Constant

Abstract

An analysis of dependences of the splitting of 4 A 2 on applied uniaxial stress P , which have been measured by authors in four expermental arrangements, P ⊥(001), P ⊥(100) and P ⊥(11 a / c ), is presented. Experimental results can be explained by strains of the [CoX 4 ] 2- complex-ion calulated by taking account not only of stiffness of the complex-ion, but also of an effective force acting on the complrx-ion itself, which is obtained expermentally from shifts of the average transition energy of spectra 4 A 2 → 2 T 2 ( 2 D ) induced by P . It is shown that the Jahn-Teller coupling constant V θ JT with the e -mode can be estimated not only from the effect of uniaxial stress, but also from the initial tetragonal distortion Δ θ i of the complex-ion. V θ JT in 4 A 2 estimated from two procidures agree with each other. The pseudo Jahn-Teller effect is expected from Δ θ i to be effective in some of excited states such as 2 E ( 2 D ), 2 T 2 ( 2 ( G ), etc., of both compounds.