Sigma‐ versus Pi‐Koordination in Bis‐indenyl‐ und Bis‐2‐methallyl‐Imidokomplexen des sechswertigen Molybdäns und Wolframs: DF‐Rechnungen und Kristallstrukturanalyse

Sigma‐ versus Pi‐Coordination in Bis‐indenyl‐ and Bis‐2‐methallyl Imido Complexes of Hexavalent Molybdenum and Tungsten: DF‐Calculations and Crystal Structure Analysis Bis‐indenyl and bis‐2‐methallyl imido complexes [(C₉H₇)₂M(NR)₂] (M = Mo, W; R = tert‐butyl, mesityl) 1 — 4 and [(H₃C‐C₃H₄)₂M(NtBu)₂] (M = Mo, W) 6 , 7 have been prepared starting from [Mo(NtBu)₂Cl₂] or [M(NR)₂Cl₂L₂] (M = W, R = tBu, L = py; M = Mo, W, R = Mes, L₂ = dme) and indenyl lithium or 2‐methallyl magnesium bromide, respectively. According to spectroscopic data and the crystal structure of 4 there are two different coordination modes of the indenyl ligands, [(η³‐C₉H₇)M(NR)₂(η¹‐C₉H₇)], in solution as well as in the solid state. These compounds show fluxional rearrangements in solution, namely σ, π‐exchange of η¹‐ and η³‐coordinated ligands. Similar behavior has been observed for the 2‐methallyl complexes 6 and 7 in solution. In agreement with experimental observations, DF calculations on models of 6 strongly suggest a (σ+π)‐coordination mode of the η³‐coordinated ligand.     

Quantum Dynamics of Li+HF/DF Reaction Investigated by a State-to-State Time-dependent Wave Packet Approach

Using the reactant coordinate based time-dependent wave packet method, on the APW potential energy surface, the differential and integral cross sections of the Li+DF/HF(v=0, j=0, 1) reactions were calculated over the collision energy range from the threshold to 0.25 eV. The initial state-specified reaction rate constants of the title reaction were also calculated. The results indicate that, compared with the Li+DF reaction, the product LiF of Li+HF reaction is a little more rotationally excited but essentially similar. The initial rotational excitation from j=0 to 1 has little effect on the Li+DF reaction. However, the rotational excitation of DF does result in a little more rotationally excited product LiF. The different cross section of both reactions is forward biased in the studied collision energy range, especially at relatively high collision energy. The resonances in the Li+HF reaction may be identifiable as the oscillations in the product ro-vibrational state-resolved integral cross sections and backward scattering as a function of collusion energy. For the Li+HF reaction, the rate constant is not sensitive to the temperature and almost has no change in the temperature range considered. For the Li+DF reaction, the rate constant increase by a factor of about 10 in the temperature range of 100?300 K. Brief comparison for the total reaction probabilities and integral cross section of the Li+HF reaction has been carried out between ours and the values reported previously. The agreement is good, and the difference should come from the better convergence of our present calculations.     

Plane‐wave density functional theory investigation of adsorption of 2,4,6‐trinitrotoluene on al‐hydroxylated (0001) surface of (4 × 4) α‐alumina

This article reports the results of the theoretical investigation of adsorption of 2,4,6‐trinitrotoluene (TNT) on Al‐hydroxylated (0001) surface of (4 × 4) α‐alumina (α‐Al₂O₃) using plane‐wave Density Functional Theory. Sixteen water molecules were used to hydroxylate the alumina surface. The Perdew–Burke–Ernzerhof functional and the recently developed van der Waals functional (vdW‐DF2) were used. The interaction of electron with core was accounted using the Vanderbilt ultrasoft pseudopotentials. It was found that hydroxylation has significant influence on the geometry of alumina and such changes are prominent up to few layers from the surface. Particularly, due to the Al‐hydroxylation the oxygen layers are decomposed into sublayers and such partitioning becomes progressively weaker for interior layers. Moreover, the nature of TNT adsorption interaction is changed from covalent type on the pristine alumina surface to hydrogen‐bonding interaction on the Al‐hydroxylated alumina surface. TNT in parallel orientation forms several hydrogen bonds compared to that in the perpendicular orientation with hydroxyl groups of the Al‐hydroxylated alumina surface. Therefore, the parallel orientation will be present in the adsorption of TNT on Al‐hydroxylated (0001) surface of α‐alumina. Further, the vdW‐DF2 van der Waals functional was found to be most suitable and should be used for such surface adsorption investigation. © 2014 Wiley Periodicals, Inc.     

Isotope E ects on Two-Photon Population Transfer Processes of HF and DF

The isotope effects of XF (X=H, D) on the population transfer process via two-photon resonance excitation are investigated by solving the time-dependent Schrödinger equation. The vibrational v =0 and 2 of the ground electronic state are taken to be the initial and target states, respectively, for the two molecular systems. The influences of the field peak amplitude and pulse duration on the population transfer process are discussed in detail. The pulse duration is required to be longer than 860 fs for the DF molecule to achieve a relatively high transfer probability (more than 80%), while the one for the HF molecule is just required to be longer than 460 fs. Moreover, the intermediate v =1 and the higher v =3 may play more important roles in the two-photon resonance process for the DF molecule, compared to the roles in the process for the HF molecule.     

发光二极管辐照光合能力快速检测系统

提出了一种以AT89c55单片机为核心实现对植物光诱导延迟荧光(DF)采集和处理的发光二极管(LED)辐照光合能力快速检测系统。该系统利用DF来表征植物的光合能力,采用DF衰减动力学曲线下面积积分作为表征方法。该系统基于弱光探测技术,采用通道光电倍增管直流模块(CPDM)来接收DF,具有很高的精度和信噪比,自带LED激发光源及温度控制,并采用小型密封暗室设计和电池供电,便于携带,可以进行现场活体测量。实验结果表明,该系统的测量精度可以达到±0.3μmol CO2m-2·s-1,具有低成本、高精度和方便实用等优点,是一种具有广阔应用前景的实用化光合能力测量仪器。     

用于泵浦非链式HF/DF化学激光器的重复频率电子束发生器研究

 正在研究的1Hz重复频率电子束泵浦HF/DF化学激光器，预期产生的电子束能量为0.5MeV、束流强度为100kA、束流脉冲宽度为100ns。在该系统设计中，使用了一个脉冲变压器来对脉冲成形水线进行双共振充电。脉冲变压器的初级、次级电感与互感分别为331nH，26.5μH与1.9μH。脉冲成形线的电容、电感与阻抗分别为8.15nF，300nH与6.2Ω。脉冲成形线在1MV的峰值充电电压下的击穿因子为0.3。在3.3%的能量转换效率条件下，预期可以产生的HF/DF激光脉冲能量为２50J以上。     

美国高能激光武器的发展及其面临的挑战(下篇)

首先介绍了美国高能激光武器的发展战略和高层技术路线(上篇)。然后分别评述了近一年来机载战区激光武器,战术高能激光武器和机载战术激光武器,天基激光武器,地基激光反卫星武器和舰载激光武器取得的重大进展,分析和讨论了它们面临的技术挑战和可能采取的对策(下篇)。     

DFHF化学激光器喷管流动数值模拟结果

模拟得到了喉部具有不同等截面段长度的二维喷管流场 ,指出了音速线随该长度的变化规律和等截面段最佳长度。模拟分析了三种不同方法设计的喷管流场和性能参数 ,结果表明新方法设计的喷管具有合适的横向速度 ,提高了喷管对F原子“冻结”效率、纵向速度等性能参数 ;能防止喷管内边界层分离和激波产生。并根据数值模拟得到的速度分布型计算了边界层位移厚度 ,讨论了DF HF激光器上述三种喷管内边界层发展规律。     

气流化学激光理论研究的若干进展

以超声速HF/DF化学激光和超声速氧碘化学激光(COIL)为代表的气流化学激光(GCL), 因其科学意义、军事和工业应用价值，近30多年来得到了突飞猛进的发展.由于超声速膨胀混合流在控制强放热反应动力学和热力学过程方面的特殊本领，使气体动力学在高功率GCL的发展中起着关键性的作用.高功率GCL性能的分析计算自然也沿用非平衡气体动力学的方法，假定气流(包括激光能级分子和原子)为连续介质，谱线为均匀加宽，并联立求解气体动力学方程组，增益动力学和基于光强迭加原则的辐射传输诸方程，称为速率方程(RE)模型.20世纪70年代后期又提出和发展了GCL性能计算的半气体动理学(SGK)模型，在SGK模型中仍假定气流为连续介质，但同时考虑了激光能级分子微观热运动的贡献，谱线加宽的非均匀加宽效应，并用双参数摄动法求解激光能级分子速度分布函数方程组(即广义Boltzmann方程组), 因此SGK模型是一个同时考虑宏观和微观尺度运动的跨尺度模型.本文综述RE模型和SGK模型以及用它们预测GCL性能的若干研究进展，同时简评等增益模型和腔模(模图样)理论研究的一些进展.最后从气体动力学的角度提出一些值得 进一步研究的课题.     

非链式化学HF(DF)激光器工作气体中电子分离的非稳定性和气体放电等离子体的自组织现象(英文)

报道了放电引发的非链式HF(DF)激光器中的激活介质由电子碰撞负离子分离引起的电离非稳定性。这种非稳性出现在电极空间分离、脉冲CO2激光加热的基于SF6的混合气体的大体积放电中。实验研究了自引发体放电过程中由激光加热引起的放电等离子体的自组织现象以及由此在放电间隙的大部分区域形成的准周期等离子体结构。重点分析了等离子体结构随气体温度和注入能量的变化,讨论了等离子体自组织对电子碰撞分离不稳定性所产生的影响,解释了混合气体中由于电子碰撞使负离子消失导致的单等离子体通道移动的产生机理。