Jahn–Teller effect in the 4T2g excited state of Cr3+ ion in Cs2NaYF6 crystal

Calculations of the fine structure of Cr³⁺ energy levels in Cs₂NaYF₆ accompanied by estimations of the Jahn–Teller (JT) stabilization energy in the first excited ⁴T_2g state of Cr³⁺ ion are presented. Two independent approaches—effective second-order spin–orbit Hamiltonian and analysis of the potential energy surfaces—are used. The JT energy was estimated to be 216 and 257 cm^–1 in the first and the second models, respectively. It is shown that the octahedral [CrF₆]^3? complex undergoes an equatorial expansion by 0.09 Å and an axial elongation by 0.02 Å due to the combined effect of the a_1g and e_g normal modes.     

Jahn–Teller effect and the formation of anticorrosive protective layers of nitrilo-tris-methylene-phosphonates on surfaces of steel

Nitrilo-tris-methylene-phosphonato-three-aqua-complexes of chromium(II) and iron(II), the main components of protective layers for inhibiting steel corrosion with nitrilo-tris-methylene-phosphonates, are isolated and studied. Their ability to form protective layers is explained by their insolubility and resistance to water and air. These properties of Cr and Fe complexes are explained by Jahn–Teller distortion of the coordination environment of Cr and Fe atoms.     

Jahn–Teller and coupled Jahn–Teller/Renner–Teller effects in the calculation of adiabatic-to-diabatic transformation angle for the lowest three 2A′ states of NH2 (NHH)

We report here on the first study of topological effects for the NHH system, as carried out by treating simultaneously the two dominant effects of this system, namely, the Jahn–Teller (JT) effect and the Renner–Teller (RT) effect. Both the effects were treated rigorously as demanded by the Born–Oppenheimer approach. No approximations were made and in those cases where convergence was required, it was achieved by including the required number of states. The study concentrates on calculating the privileged adiabatic-to-diabatic transformation (ADT) angle γ_12, along closed contours, which is the only needed angle to carry out the ADT in the case of relatively low energies. For this purpose, three coupled A′-states are usually considered and only in the last two extreme cases, where the area in configuration space becomes relatively large, namely 15–35 Ų, we had also to include an A^″ state (the second Δ-state), a situation that enforces the more elaborate (JT/RT) effect. In this paper, we also report on potential energies as calculated along the above-mentioned contours. Among them are considered the energies associated with the two adiabatic Δ-states, 1A′ and 1A^″, of different symmetry and therefore are responsible for the RT effect. These states are expected to be degenerate along the collinear axis. It was revealed that these states, in contrast to the Renner theory, are not degenerate along a finite interval of the collinear axis at the vicinity of the JT conical intersection (JT-CI). In other words, the JT-CI annihilates the RT degeneracy along this interval.     

The role of the second order Jahn–Teller effect in the thermal reactions of ethylene

The UV absorption spectrum of ethylene during the pulse heating of an ethylene–argon mixture to prepyrolysis temperatures in the range 950 < Т < 1285 K was studied by kinetic spectroscopy in a free-piston adiabatic compression unit. New intense light absorption bands were found at 210 < λ < 260 and 440 < λ < 490 nm. Ab initio quantum-chemical calculations of the mechanism of the thermal cis-trans isomerization of ethylene were performed. When this mixture is heated, the point symmetry group of the ethylene molecule in the ground state S₀ reduces to С ₁, which is characteristic for ethylene at the minimum of the S ₁ state, due to the second order Jahn–Teller effect.     

Tunneling Relaxation Mechanisms of the Jahn–Teller Complexes in a CaF2:Cr2+ Crystal

JETP Letters - The temperature dependences of attenuation and the velocity of ultrasonic waves at frequencies of 26–158&nbsp;MHz in a CaF2 fluorite crystal at the substitution of...     

Construction of the Γ9 × (g+ 2h) Jahn–Teller Hamiltonian

The coupling coefficients describing the linear Γ ₉× (g+2h) Jahn–Teller Hamiltonian in icosahedral symmetry are derived, and various coupling schemes are discussed.     

Jahn–Teller Cr2+ Centers in a CdSe Crystal

Physics of the Solid State - Impurity Cr2+ ions in the CdSe crystal are studied by tunable EPR spectroscopy in the frequency range of 70–320 GHz. The discovered Jahn–Teller tetragonal...     

Spin-Hamiltonian parameters and tetragonal distortion due to the Jahn–Teller effect for Cu2+ centres in trigonal Zn(BrO3)·6H2O crystal

The spin-Hamiltonian parameters (g factors g_//, g_⊥ and hyperfine structure constants ⁶⁵A_// and ⁶⁵A_⊥) for the tetragonal Cu²⁺ centres in trigonal Zn(BrO₃)·6H₂O crystal are calculated from the complete diagonalization (of energy matrix) method (CDM) based on the cluster approach. In the CDM, the Zeeman and hyperfine interaction terms are added to the Hamiltonian in the conventional CDM and the contributions to the spin-Hamiltonian parameters from both the spin-orbit coupling parameter of central d⁹ ion and that of ligand ion are included. The calculated spin-Hamiltonian parameters of Zn(BrO₃)·6H₂O: Cu²⁺ show good agreement with the experimental values and the tetragonal elongation (characterized by ΔR=R_// ? R _⊥, where R_// and R _⊥ represent the metal-ligand distances parallel with and perpendicular to the C₄ axis) due to the static Jahn–Teller effect is obtained from the calculations. The results are discussed.     

Determining the Parameters of the Jahn–Teller Effect in Impurity Centers from Ultrasonic Experiments: Application to the ZnSe : Ni2+ Crystal

Physics of the Solid State - The earlier developed methodology of ultrasonic investigation for determining the parameters of the Jahn–Teller effect (JTE) in impurity centers in crystals is...     

Ultrasonic Determination of the Jahn–Teller Effect Parameters in Impurity-Containing Crystals

Journal of Experimental and Theoretical Physics - A method is developed to determine the symmetry properties of strains and the type of Jahn–Teller effect in crystals with impurity ions in a...     

Jahn—Teller coupling in the [Xtilde] 2E ground states of the CF3O and CF3S radicals

The Jahn—Teller and spin—orbit coupling in the ground states of the CF₃O and CF₃S radicals have been investigated experimentally by dispersed fluorescence spectroscopy. These spectra are analysed using a theoretical model that simultaneously includes spin—orbit coupling and multimode Jahn—Teller coupling, both linear and quadratic. We find that in each of these radicals a moderate linear Jahn—Teller effect exists in ν₆, with a much smaller coupling in ν₅. These results are compared and contrasted with those for the related radicals CH₃O and CH₃S. The experimental data and theoretical analyses of these four radicals represent the most thorough investigations to date of the combined effects of spin—orbit and Jahn—Teller coupling.     

Contribution from structural Jahn–Teller ions to the elastic and ferroelectric properties of lithium niobate and lithium tantalate

Elastic and ferroelectric characteristics of single crystals of lithium niobate and tantalate are investigated in a wide range of temperatures by complex acoustooptic means. The contribution from Jahn–Teller NbO₆ and TaO₆ systems to the characteristics of elastic moduli, ultrasonic attenuation, and nonlinear optical coefficients is analyzed using a new phenomenological model. It is hypothesized that the displacement of Nb⁵⁺ and Ta⁵⁺ ions, which exhibit the second-order Jahn–Teller effect along trigonal axis C, and the subsequent ordering of octahedral, result in unusual elastic and ferroelectric properties.