Is it possible to use Charge Transfer Bands to Measure Impurity-Ligand Distances? Experimental and Theoretical Results on Cu 2+ Doped (C 2 H 5 NH 3 ) 2 CdCl 4

The present work is focused on the effects produced by hydrostatic pressure on Cu 2+ (<100 ppm) doped (C 2 H 5 NH 3 ) 2 CdCl 4 single crystal. The energy E u ( ~ ) of the e u ( ~ ) M b 1 g (～ x 2 m y 2 ) charge-transfer transition of (C 2 H 5 NH 3 ) 2 CdCl 4 : Cu 2+ undergoes a red shift of 1400 cm m 1 on passing from ambient pressure to 40 kbar. To understand this fact theoretical calculations of the {\rm CuCl}^{4-}_{6} complex using four different methods have been carried out. Based on these calculations, it is concluded that the experimental red shift undergone by E u ( ~ ) can only be reasonably explained through a decrease of ～25 pm in R ax and an increase of ～7 pm in R eq leading to a decrement of the {\rm CuCl}^{4-}_{6} volume. Variations of any metal-halide distances down to 0.1 pm can be well detected through the shifts of the charge-transfer band energy upon pressure.     

B2H6分子在C2v势阱中的频率分解及其各向异性效应

依据杨-泰勒效应理论、量子理论和群论探讨了具有D3h对称性构型的B2H6分子的E  e′系统在C2v势阱中的频率分解及其各向异性现象。借助么正平移变换和标度变换计算出了杨-泰勒畸变后的系统振动频率,结果表明,畸变导致系统二重简并的振动模式e′的振动频率发生了分解,对于系统的4个C2v势阱而言,无论系统处在哪一个势阱中,畸变所导致的频率分解都是相同的;畸变同时还导致系统的振动基态能量比畸变前降低了。正是这种基态能量的降低,使得畸变后系统就达到了一个更加稳定的状态。文中利用群论进一步探讨了系统的频率分解,结果发现,畸变导致系统的二重简并振动态e′分解为两种非简并的振动态,它们分别具有C2v群下的a1与b2对称性。系统的频率分解与基态能量的降低就意味着系统的各向同性遭到破坏而呈现出各向异性。     

C42+分子的T  e系统的Jahn-Teller效应与各向异性现象

依据Jahn-Teller效应理论与量子理论,利用群论和对称性分析的方法探讨了具有Td对称性构型的C42+分子的T  e 系统的Jahn-Teller效应与各向异性问题。构建了T  e系统的电声耦合哈密顿量,借助么正平移变换求出了系统的基态与激发态及其能量。结果发现,由于电声耦合作用的缘故,系统发生了Jahn-Teller畸变,畸变导致在系统的势能面上形成了3个具有D2d对称性的势阱。无论系统处在哪一个势阱中,系统原初三重简并的能级都将分裂为两条能级。畸变还导致C42+分子从Td对称性降低到D2d对称性,同时C42+分子的振动频率发生分解,而频率的分解致使C42+分子的各向同性遭到破坏而呈现出各向异性。     

一价Na元素对LaMnO3母体A位掺杂的磁电性质的影响

通过测量La1-xNaxMnO3(x=0.05、0.10、0.15、0.20、0.25、0.33)体系的M～T曲线和R～T曲线,研究了La位Na掺杂对体系磁电性质的影响.结果发现:随着Na掺杂浓度的增加,体系居里温度Tc升高,顺磁-铁磁相变逐渐变陡;伴随着顺磁-铁磁相变,体系发生金属-绝缘体相变,电阻随掺杂浓度增加而下降.体系磁电性质的变化来源于掺杂引起的Mn3 -O-Mn4 间的双交换作用、静态Jahn-Teller畸变和公差因子的变化.     

Towards a theory of dissociative recombination

Current experiments in storage rings at Aarhus and Stockholm reveal that ions such as CH ₃ ⁺ , OH ₃ ⁺ , OH ₂ ⁺ and CH ₅ ⁺ recombine and fragment into three parts more often than into just two. Analysis of the possible resonances between free electron and bound electron states for the ions require a detailed examination of the correlation effects as well as the coupling to nuclear degrees of freedom. The problem is well suited for the propagator approach. An analysis of the structure of the self-energy kernel shows the presence of possible resonances with degenerate electronic states which are unstable according to the Jahn-Teller theorem and provides channels for multiple fragmentation.     

A comparative study of high-spin manganese and iron complexes

Different metal complexes of the general form M(OH) _n (H₂O)_{6– n} have been studied for manganese and iron. Oxidation states considered for manganese are Mn(III), Mn(IV) and Mn(V) and for iron Fe(II), Fe(III) and Fe(IV). Oxygen containing ligands are used throughout with varying numbers of hydroxyl and water ligands. Some metal-oxo and some charged complexes were also studied. Large Jahn-Teller distortions were found for the Mn(III) and Fe(IV) complexes. Consequences of these distortions are that water ligands have to be placed along the weak JT-axis and that five-coordination by a loss of one of these water ligands is quite competitive with six-coordination in particular for manganese. For Fe(II) and Fe(III) lower coordinations than six are preferred due to the presence of two repulsive e _g electrons. For the metal-oxo complexes five-coordination is also preferred due to the strong trans effect from the oxo ligand. All complexes studied have high-spin ground states. An interesting effect is that the spin is much more delocalized on the ligands for the iron complexes than for the manganese complexes. This effect, which is chemically important for certain iron enzymes, is rationalized by the large number of 3d electrons on iron. For manganese with only five 3d electrons no spin delocalization is needed to obtain the proper high-spin states. Received: 4 February 1997 / Accepted: 24 February 1997     

Potential energy profiles along the doubly degenerate vibrational modes in conjugated molecules

In order to predict the molecular symmetries and the geometrical structures of conjugated molecules having the doubly degenerate first-order Jahn-Teller active modes (Q ₁ and Q ₂) or the doubly denegerate modes through which the second-order vibronic couplings occur (Q₁ and Q₂), the potential energy curves along these modes are expressed as the power series, including up to the third power. It is shown that although there are cases in which we cannot practically differentiate between the potential energy profiles along Q ₁, and Q ₂ or Q₁ and Q₂, in so far as we can differentiate between them, a potential energy minimum should always be located along Q ₁ or Q₁ that distorts a molecule in a more symmetrical way. This is in agreement with the available experimental facts. Finally on the basis of the perturbation theory, the coefficients of various powers (up to the third power) in the expansion of the electronic part of potential energy in the power series of the relevant mode are expressed in terms of the zeroth-order electronic wavefunctions and energies.     

The role of orbital ordering in the tetragonal-to-cubic phase transition in CuCr2O4

Copper(II) chromite (CuCr₂O₄) undergoes a first-order structural transition from a tetragonal distorted spinel structure in space group (I4₁/amd) to a cubic spinel structure in Fd3¯m, near 600 °C. The transition has been followed using synchrotron X-ray powder diffraction between room temperature and 750 °C. The structure changes as a consequence of a transition from an orbitally ordered to orbital disordered state associated with a Jahn-Teller-type distortion of the CuO₄ tetrahedron. The orbital melting results in a small increase in cell volume.     

The effect of chromium substitution on the phase transition of lithium manganese spinel oxides

The phase transition of chromium substituted lithium manganese spinel oxide, LiCr_yMn_2−yO₄ was investigated by low-temperature powder X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and electrical resistivity measurements. The sample prepared at 820 °C resulted in lowering the transition temperature T_t with Cr composition y, whereas T_t of the sample prepared at 750 °C remained constant for 0≤y≤0.17 in LiCr_yMn_2−yO₄. This would be caused by a difference in distribution of the substituted Cr³⁺ ion in octahedral site depending on the preparation temperature. The phase transition was suppressed with increasing the amount of Cr content.     

具有D4h对称性构型的C2+4分子的Jahn-Teller效应与能级分裂

依据量子理论与配位场理论,利用群论和对称性分析的方法探讨了C²⁺₄分子在具有D_4h对称性构型时,E×(b_1g+b_2g)系统的Jahn-Teller效应中的相关问题.研究了C²⁺₄分子的电子态与声子态的对称性及其活跃声子态,讨论了系统声子间的耦合与CG系数,构建了E×(b_1g+b_{2g 关键词： 2+4分子')" href="#">C²⁺4分子 对称性 能级分裂 Jahn-Teller畸变}