The Degenerate Vibrations of BCl3, BBr3 and BI3 with Application of Keating Coordinates

The experimental works of vibrational spectroscopy and normal coordinate analyses for BCl₃, BBr₃ and BI₃ are reviewed extensively. Harmonic force fields of the E' species are produced using isotopic frequencies and Coriolis constants as additional data, respectively. The usefulness of Keating coordinates versus valence coordinates as basis of force field approximations is discussed. The conclusions are not unequivocal, but they go in favour of the Keating coordinates when the reliability of the different computations is taken into account. Boron trichloride is treated specifically in some detail. Final force fields are proposed for the title molecules with the aid of the mass influence on Coriolis constants.     

Relation Between Laser Induced Infrared Fluorescence and Laser Absorption By Pollutant Gases

Symmetry coordinates were developed for the dodecaborane-ion type X₁₂Y¹² model of symmetry I_h. Two sets of force constants for the ion are reported, where it was made use of Decius' and Keating's bendings, respectively. Calculated frequencies for B₁₂H₁₂ and B₁₂D₁₂ are compared with observed data. Better agreement was obtained for the set with Keating's bendings. This conclusion is consistent with one of a previous normal coordinate analysis.     

Application of the Keating Bendings to the In-Plane Vibrations of Naphthalene and Benzene

An approximate force field was deduced for the in-plane vibrations of naphthalene in terms of five parameters corresponding to the coordinates: C-C and C-H stretchings, CCC (two types) and CCH Keating's bendings. Calculated frequencies were compared to observed data. On the other hand, these results were compared to those where Decius' bendings were applied. The set with Keating's bendings proved to be the superior one.

The corresponding force fields were applied to benzene, and the same general conclusion was reached.     

利用Keating模型计算Si（1-x）Gex及非晶硅的拉曼频移

利用Keating模型计算了Si_（1-x）Ge_x合金中Si—Si,Ge—Ge和Si—Ge三种振动模态的拉曼频移,计算分别获得Ge浓度为01,05和09时,Si—Ge的振动拉曼频移分别为40275,41339和38815 cm^-1,这些结果与文献的实验结果符合,证明了Keating模型建立的关于原子振动模型是有效的,并可以利用拉伸压缩和相邻原子键之间弹性系数变化获得处于应变状态的拉曼光谱频率.利用Kea 关键词： Keating模型 拉曼光谱 （1-x）Ge_x')" href="#">Si_（1-x）Ge_x 非晶硅     

A Simple Force-Field Approximation Applied to the In-Plane Vibrations of Some Condensed Aromatics

In-plane vibrational frequencies of five condensed aromatics were computed from a five-parameter force field pertaining to stretchings and Keating's bendings. The molecules are: anthracene, phenanthrene, pyrene, chrysene and coronene. The results were compared with previous ones from a five-parameter approximation, which employs Decius' bendings. As far as the agreement between calculated and observed frequencies are concerned the results with Keating's bendings appeared clearly to be the superior ones in all the cases investigated.     

XF2(X=B,N)分子基态的结构与势能函数

基于Gaussian03计算软件利用QCISD方法,选用不同基组对XF₂(X=B,N)分子基态结构进行了几何优化,在此基础上选出最优基组D95(df,pd)和D95+(df,pd)分别对BF₂和NF₂分子的谐振频率、力常数等进行了计算.推导出XF₂(X=B,N)分子基态的多体展式势能函数,同时根据势能函数绘制了XF₂(X< 关键词： 2')" href="#">BF₂ 2')" href="#">NF₂ 结构 势能函数     

Electron diffraction data as a constraint in the determination of force field of thallous halide dimers

Electron diffraction data have been used as a constraint in the determination of force field for Tl₂F₂ having planar rhombic structure. The L-F approximation method, recently given by us, has also been applied to evaluate force constants for thallous halide dimers,e.g. T1₂F₂ and T1₂Cl₂. The results have been compared with the available experimental data in order to check the validity of the present work. It is concluded that non-bond experimental mean amplitudeU ₁..._Tl for Tl₂F₂ is capable of fixing the force field and L-F approximation gives reasonably good force fields for the two thallous halide dimers now under study.     

β-Si3N4电子结构和红外和拉曼频率的第一性原理研究

分别用PW91,B3LYP两种密度泛函方法和全电子高斯基组对β-Si₃N₄的几何结构进行全优化(包括晶格参数和原子坐标),结果和实验值符合良好. 同时计算了能带结构和态密度.在此基础上分别用上述两种方法计算了Γ点拉曼振动频率,并按对称性进行分类,将得到的11种拉曼活性模式的频率值与实验值以及其他文献值进行了比较,进一步确定了A_g模式为中等频率,值约459cm^-1. 计算结果表明 关键词： 振动频率 密度泛函理论 电子结构 3N₄')" href="#">β-Si₃N₄     

Exchange charge model and analysis of the microscopic crystal field effects in KAl(MoO4)2:Cr

In the present paper, we report on consistent crystal field calculations of the Cr³⁺ ions energy levels in KAl(MoO₄)₂ using actual D_3d site symmetry of the Cr³⁺ position and employing the exchange charge model (ECM) of the crystal field. In addition to the energy level calculations, the Huang-Rhys factor S=5.7 and effective phonon energy ?ω=268 cm^-1 were evaluated in the single configurational coordinate model. Detailed treatment of the microscopic crystal field effects in the ECM framework allowed to obtain analytical dependence of the crystal field strength 10Dq on the Cr-O interionic distance and extracting from it the values of some parameters of the electron-vibrational interaction (EVI) in the KAl(MoO₄)₂:Cr³⁺ system. All obtained results are compared with experimental data and discussed; agreement between the calculated and experimental parameters is good.     

Normal Coordinates Analysis for The M(NH3)2+ 4 Complex Ions in D4h and Td Symmetries. Simplified Molecular Models

A normal coordinates analysis for the M(NH₃)²⁺ ₄ complex ions in T_d symmetry (M = Zn, Cd, Co) and in D_4h symmetry (M = Cu, Pd, Pt) has been undertaken on the basis of a General Valence Force Field (GVFF), using simplified molecular models. Throughout the course of the present work, we have relaxed the point mass approximation for the NH₃-ligands in order to investigate, on a quantitative basis, some relevant ligand - framework coupling vibrations. The simplest molecular model able to accomplish this purpose is to treat the ammino group, in a linear ligator approximation. We show that these model calculations provide a satisfactory set of vibrational frequencies as well as consistent sets of force constants.     

The ro-vibrational analysis of the v4 fundamental band of CF3Br from jet-cooled diode laser and FTIR spectra in the 8.3-μm region

The v₄ fundamental band of CF₃⁷⁹Br and CF₃⁸¹Br, present in natural isotopic abundance, was investigated in the 8.3-μm region by high-resolution infrared spectroscopic techniques. Tuneable diode laser spectra were recorded in the ranges 1202.5–1205.0 cm^?1, 1208.0–1210.1 cm^?1 and 1212.5–1214.5 cm^?1. The tuneable diode laser spectra were obtained at the reduced temperature of 200 K and in a free-jet expansion. The latter technique was used to reduce spectral congestion, achieving a rotational temperature of about 50 K, with a resolution up to 0.0008 cm^?1. A Fourier transform infrared spectrum covering the entire spectral region of the v₄ band, between 1190 and 1220 cm^?1, was recorded at 298 K with a resolution of 0.004 cm^?1. The experimental wavenumbers from the different spectroscopic techniques were combined to accomplish the complete ro-vibrational analysis of v₄. In total, 4651 transitions were assigned to CF₃⁷⁹Br, 4047 to CF₃⁸¹Br, with J″_max? = K″_max?=80; of these, 3171 for CF₃⁷⁹Br and 2755 for CF₃⁸¹Br are from diode laser measurements. The data of each isotopologue were analysed using the model Hamiltonian for a degenerate vibrational state of a molecule of C_3v symmetry. The v₄ band of both the isotopologues resulted essentially unperturbed, but the Δl = Δk = ±2 l-resonance was found to be active within the v₄ = 1 state. Precise values of the vibrational energy and of the ro-vibrational parameters of v₄ = 1 for CF₃⁷⁹Br and CF₃⁸¹Br were obtained. The bromine isotopic splitting amounts to 6.9 × 10^?3 cm^?1. In addition, the equilibrium geometry and the harmonic force field were calculated ab initio using the large-size basis set def2-QZVP in conjunction to the PBE0 functional.     

Studies of the optical spectra and spin-Hamiltonian parameters for the trivalent ytterbium ions in lithium yttrium fluoride crystals

In this paper, the crystal field (CF) levels and spin-Hamiltonian (SH) parameters (g factors g _∥ and g _⊥ and hyperfine structure constants A _∥ and A _⊥) of the rare-earth ion Yb³⁺ in lithium yttrium fluoride crystals are calculated under D _2d point symmetry assumption. Two main methods are used in the calculation to study the SH parameters: one is the perturbation theory method and the other is the complete diagonalization (energy matrix) method (CDM). Comparing the calculated results with the experimental data, we can see that the CDM is more effective to calculate the SH parameters. In addition, the CF J-mixing of all excited-state multiplets into the ground-state multiplet ²F_7/2 is considered. The validity of the calculated results is discussed.     

Normal Coordinate Analysis of the Tricyanomethanide ion C(CN)− 3 (D3h)

Abstract

A complete normal coordinate analysis has been performed for the tricyanomethanide ion C(CN)^? ₃ for which a planar structure of symmetry D_3h was assumed. The symmetric Fand internal f valence force constant matrices were derived in the general case by using a GVFF and the results are applied to C(CN)^? ₃.     

Effect of adding Ar gas on the pulse height distribution of BF<Subscript>3</Subscript>-filled neutron detectors

Boron trifluoride (BF₃) proportional counters are used as detectors for thermal neutrons. They are characterized by high neutron sensitivity and good gamma discriminating properties. Most practical BF₃ counters are filled with pure boron trifluoride gas enriched up to 96% ¹⁰B. But BF₃ is not an ideal proportional counter gas. Worsening of plateau characteristics is observed with increasing radius due to impurities in gas. To overcome this problem, counters are filled with BF₃ with an admixture of a more suitable gas such as argon. The dilution of BF₃ with argon causes a decrease in detection efficiency, but the pulse height spectrum shows sharper peaks and more stable plateau characteristics than counters filled with pure BF₃. The present investigations are undertaken to study the pulse height distribution and other important factors in BF₃+Ar filled signal counters for neutron beam applications. Tests are performed with detectors with cylindrical geometry filled with BF₃ gas enriched in ¹⁰B to 90%, and high purity Ar in different proportions. By analysing pulse height spectra, a value of 6.1 ± 0.2 has been obtained for the branching ratio of the ¹⁰B(n,α) reaction.      

Theoretical studies of the spin Hamiltonian parameters and local structures for WO3 doped Zn3(PO4)2ZnO nanopowders

The spin Hamiltonian parameters (SHPs) and the local structures for impurity W⁵⁺ in the Zn₃(PO₄)₂ZnO nanopowders doped with WO₃ under different concentrations are theoretically investigated using the perturbation calculations of these parameters. The exponential functions of the related quantities (cubic field parameter Dq, covalency factor N, relative tetragonal compression ratio τ and core polarisation constant κ) of concentration x with totally four adjustable coefficients a, b, c and d are adopted to fit the concentration dependences of the experimental d-d transition bands and SHPs. The impurity W⁵⁺ centres demonstrate moderate tetragonal compression ratios τ (～3.1%) due to the Jahn–Teller effect. With the increase of WO₃ concentration, Dq and N show moderately decreasing rules, while τ and κ exhibit slightly and moderately increasing tendencies with x, respectively. The mechanisms of the above concentration dependences of these quantities are analysed from the modifications of the local crystal-field strength and electron cloud density around the impurity W⁵⁺ with the variation of x. Present theoretical studies would be useful to the exploration of the structural properties and optical applications for WO₃ doped Zn₃(PO₄)₂ZnO nanopowders.     

White light generation through the zinc metaphosphate glass activated by Ce, Tb and Mn ions

The photoluminescence of Ce³⁺, Tb³⁺ and Mn²⁺ ions was investigated in the Zn(PO₃)₂ glass. The blue and green emissions of Tb³⁺ ions and the red emission of Mn²⁺ ions are enhanced upon UV excitation through a non-radiative energy transfer from Ce³⁺ to Tb³⁺ and Mn²⁺ ions. The efficiency of this transfer was estimated in at least 62%. It is demonstrated that this glass activated with three ions (Ce³⁺, Tb³⁺ and Mn²⁺) can generate white light emission (x=0.420 and y=0.423 chromaticity coordinates and 3440 K colour temperature) under excitation at 254 nm, i.e., using an AlGaN-based LED as excitation source.     

Luminescence properties of cerium-doped di-strontium magnesium di-silicate phosphor by the solid-state reaction method

A series of Sr₂MgSi₂O₇:xCe³⁺ (x?=?1.0%, 2.0%, 3.0%, 4.0% and 5.0%) phosphors were synthesized by the solid-state reaction method. The phosphor with optimum thermoluminescence, photoluminescence and mechanoluminescence (ML) intensity was characterized by X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared techniques. The trapping parameters (i.e. activation energy, frequency factor and order of the kinetics) of each synthesized phosphor have been calculated using the peak shape method and the results have been discussed. Under ultraviolet excitation (325?nm), Sr₂MgSi₂O₇:xCe³⁺ phosphors were composed of a broad band peaking at 385?nm, belonging to the broad emission band which emits violet-blue color. Commission International de I’Eclairage coordinates have been calculated for each sample and their overall emission is near violet-blue light. In order to investigate the suitability of the samples for industrial uses, color purity and color rendering index were calculated. An ML intensity of optimum [Sr₂MgSi₂O₇:Ce³⁺ (3.0%)] phosphor increases linearly with increasing impact velocity of the moving piston which suggests that these phosphors can be used as fracto-ML-based devices. The time of the peak ML intensity and the decay rate did not change significantly with respect to increasing impact velocity of the moving piston.     

Studies of the g factors and the local structure for Ni3+ in LaAl0.9Ni0.1O3, La0.75Y0.25Al0.99Ni0.01O3 and YAl0.9Ni0.1O3

The electron paramagnetic resonance g factors and the local structure for Ni³⁺ in LaAl_0.9Ni_0.1O₃ (LAN), La_0.75Y_0.25Al_0.99Ni_0.01O₃ (LYAN) and YAl_0.9Ni_0.1O₃ (YAN) are theoretically studied from the perturbation formulas of the g factors for a 3d⁷ ion of low spin (S = 1/2) in tetragonally elongated octahedra. In these formulas, the contributions to the g factors from the tetragonal distortion, characterized by the tetragonal field parameters Ds and Dt are taken into account. According to the calculations, the ligand octahedra around Ni³⁺ are suggested to suffer 2% relative elongation along the [001] (or C₄) axis due to the Jahn-Teller effect.     

Calculations of the optical and EPR spectral data for Cr3+ ion in Y3Ga5O12 crystal from the complete diagonalisation method

The complete diagonalisation (of energy matrix) method is applied in this paper to calculate together the optical and electron paramagnetic resonance (EPR) spectral data for Cr³⁺ ion at the trigonal Ga³⁺ site of Y₃Ga₅O₁₂ crystal. The method is founded on the two-spin-orbit-parameter model where in addition to the contributions from the spin-orbit parameter of central dⁿ ion (i.e., one-spin-orbit-parameter model) in the traditional crystal field theory, those from the spin-orbit parameter of ligand ion via covalence effect is also considered. The calculated results propose that by using only four adjustable parameters, the 12 observed spectral data (nine optical band positions and three EPR parameters g_//, g_⊥ and D) in Y₃Ga₅O₁₂: Cr³⁺ are reasonably explained. The impurity-induced local lattice distortion of Cr³⁺ in Y₃Ga₅O₁₂ crystal is also estimated through the calculations. The results are discussed.