An electron-diffraction study of the molecular structure of gaseous perbromyl fluoride and calculation of its force field and vibrational amplitudes

The molecular structure of FBrO₃ has been studied by gas-phase electron diffraction. Least-squares refinements of the molecular geometry using fixed spectroscopic amplitudes revealed two geometrical minima. Initially, the amplitudes employed were derived from diagonal force fields obtained by spectroscopic least-squares refinements to fit observed and calculated wave numbers; for each geometry there are two spectroscopic minima. In the lowest geometrical minimum the wave number agreement is poor, however, the introduction of the ∠OBrO/∠FBrO interaction force constant removed the discrepancies; the resulting force field is F(Br-O) = 6.92 ± 0.02 mdyn Å^?1F(Br-F) = 3.22 ± 0.03 mdyn Å^?1, F(∠OBrO) = 1.06 ± 0.02 mdyn Å, F(∠FBrO) = 0.81 ± 0.03 mdyn Å, F(∠OBrO/∠FBrO) = ?0.19 ± 0.02 mdyn Å. In the corresponding geometrical minimum r_g(Br-O) = 1.582 ± 0.001 Å, r_g(Br-F) = 1.708 ± 0.003 Å, r_α(∠OBrO) = 114.9 ± 0.3°, r_α(∠FBrO) = 103.3 ± 0.3°. Perpendicular amplitude correction coefficients, calculated for each force field employed, were used throughout to relate the interatomic distances through the r_α-structure. The geometries of the r_α^o- and r_e-structures are estimated.     

Structural chemistry of bimetallic hydride complexes of titanium and aluminium: I. Crystal and molecular structure of [(η5-C5H5)2,Ti(μ-H)2AlH2]2(CH3)2NCH2CH2N(CH3)2C6H6

The structure of a titanium aluminium hydride complex of composition [(C₅H₅)₂TiAlH₄]₂(CH₃)₂NC₂H₄N(CH₃)₂C₆H₆ has been determined by X-ray diffraction. The complex forms triclinic crystals with unit cell dimensions a = 8.406(2), b = 10.117(2), c = 11.269(3) Å; α = 112.01(2)°, β = 109.25(2)°, γ = 87.04(2)°, space group P$\text{1}$, Z = 2 and density d = 1.21 g/cm³. The structure was refined to give a discrepancy index R = 0.056. The crystals are composed of centrosymmetric molecules of (Cp₂TiAlH₄)₂TMEDA (Cp = η⁵-cyclopentadienyl) and molecules of crystal benzene. Two moieties of Cp₂TiH₂AlH₂ are linked by a tetramethylethylenediamine molecule (r_AlN 2.11 Å). The aluminium atom is bonded to a titanium atom by a double hydride bridge (r_AlH b = 1.8, 1.6 Å, r_TiH b = 1.6 Å), and has trigonal bipyramidal stereochemistry, [H₄N] (r_AlH t = 1.6 Å).     

Relative raman line intensities for H2 and for D2. Correction factors for molecular non-rigidity

Ab initio calculations are presented for H₂ and D₂ relative Raman intensities originating from common rotational levels for both vibrational-rotational and pure rotational transitions. Factors f(J) required to correct measured intensities for molecular non-rigidity (e.g. in temperature measurements) are tabulated. The calculations are compared with literature perturbation-theory equations (significant differences at large J in vibration-rotation) and with experiment.     

Molecular structure of carbonyl bromide as studied by gas electron diffraction

The molecular structure of COBr₂ has been determined as follows by an analysis of electron diffraction intensity: r_g(CO) = 1.178 ± 0.009 Å, r_g(C-Br) = 1.923 ± 0.005 Å and θ°_α(Br-C-Br) = 112.3 ± 0.4°. The uncertainties represent estimated limits of error. The observed systematic trends in the bond lengths and bond angles in carbonyl and thiocarbonyl halides are discussed.     

大气混合层厚度的计算方法及影响因子

本文讲述了大气混合层厚度的定义及它在大气环境保护中的作用。论述了大气混合层厚度的多种计算方法如国标法、干绝热法、罗氏法等，并分析了大气混合层厚度的各种影响因子。其中大气稳定度是决定混合层厚度的最主要因子。     

陕西长青自然保护区鱼类资源及其多样性

陕西长青国家级自然保护区共有鱼类 18种 ,隶属于 5目 7科 .主要经济鱼类有拉氏鱼岁、多鳞铲颌鱼、马口鱼、红尾副鳅和黑鳍鱼泉 .海拔越高 ,鱼类种类越少 ,多样性越低 ;鱼类的多样性还与人类的活动密切相关 .本区分布的细鳞鲑为国家Ⅱ级保护野生动物 ,现已移入酉水河上游 ,进行自然增殖 .     

民族地区高校统计工作存在的问题及对策

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庞泉沟自然保护区种子植物区系研究

庞泉沟保护区有种子植物81科344属806种。其中野生种有786种;裸子植物2科6属9种,分别占全国同类别的20%,15%,4.7%;被子植物79科338属797种,分别占全国同类别的27%,11%,2.97%。科的分布区类型以世界分布的科占优势,占种子植物总科数的44.44%,其次是温带分布。属的分布区类型以温带成分占绝对优势,其中北温带分布型占的百分比最高,占本区种子植物区系中非世界属数的50%。     

湖南省蝶类新纪录

2016年4-10月对湖南黄桑国家级自然保护区的蝶类资源进行了逐月调查，共记录到蝴蝶3 611只，隶属5科96属170种.经鉴定其中6种为湖南省新纪录种，分别是红斑翠蛱蝶Euthalia lubentina Cramer、白钩蛱蝶Polygonia c-album Linnaeus、灿烂双尾灰蝶Tajuria luculenta Leech、咖灰蝶Catochrysops strabo Fabricius、婀玛灰蝶Mahathala ariadeva Fruhstorfer和晓徘弄蝶Pedesta xiaoqingae Huang et Zhan.     

“全国文学创作”山西中心选址方案的合理性探讨

在分析"全国文学创作"山西中心项目建设的依据及必要性基础上,从选址方案的规划、交通、市政基础设施等方面,对选址方案的合理性进行了探讨。