Theoretical study of the new compound VO2 (D)

The structural feature and the electronic properties of the newly synthesized compound VO₂ (D) are theoretically studied. Our calculations reveal that all of the V ions in VO₂ (D) form two types of chains. One of the chains contributes to the electronic states near the Fermi level, but the other one almost does not yet. Such discrepancy is attributed to the different strength of the VO bonds belonging to the different chains. Furthermore, it is found that one type of the VV chains characters the antiferromagnetic feature, whereas the other one is almost non-magnetic. So, the compound VO₂ (D) is of one-dimensional antiferromagnetic ordering. In addition, we propose that the structural transition from VO₂ (D) to the rutile-type VO₂ (R) is driven by three vibrational modes. The transition temperature is estimated to be about 600 K, being consistent with experiment.     

RbH(X1∑+,v=O～2)能级与H2碰撞振动能量转移

利用积分时间分辨荧光光谱方法,研究了RbH(X1Σ+,v=0～2)与H2间的振动碰撞能量转移。在Rb-H2混合样品池中,泵浦激光双光子激发Rb原子至6D态,Rb(6D)与H2反应生成RbH(X1Σ+)分子,探测激光延迟泵浦激光20ns,通过激光感应荧光光谱(LIF)的测量,确定了X1Σ+(v=0～2,J)原生态的转动布居分布。增加检测激光与泵浦激光的延迟时间,测量了0～10μs延迟时间内各振动态时间分辨LIF强度,v=0,1能级荧光信号先增加后缓慢减弱,这是因为RbH在瞬间形成后通过碰撞转移和扩散而减少所致。通过速率方程分析,并利用振动能级上布居数变化与积分时间分辨荧光强度的关系,得到v=1→v=0和v=2→v=1的碰撞转移速率系数分别为(2.8±0.6)×10-11cm3·s-1和(3.4±0.8)×10-11cm3·s-1。而v=0,1,2的扩散率分别为(4.9±1.1)×105,(1.0±0.3)×105,(0.6±0.2)×105s-1。实验表明,v=2能级上布居数衰减率最大。     

介质阻挡放电中圆圈点放电丝的分子振动温度

在氩气、空气混合气体介质阻挡放电中,首次利用光谱方法,测量了圆圈点放电丝中圆圈放电和中心点放电的振动温度,并研究了它们随空气含量的变化.振动温度的计算利用的是氮分子第二正带系(C3Ⅱu→B 3Ⅱg)的发射谱线.结果表明:圆圈放电的振动温度高于中心点放电的振动温度;二者均随空气含量的增加而增加,但圆圈放电振动温度的增加速...     

Liquid Space Lubricants Examined by Vibrational Microspectroscopy

Abstract

Considerable effort has been expended to develop liquid lubricants for satellites and space exploration vehicles. These lubricants must often perform under a range of harsh conditions such as vacuum, radiation, and temperature extremes while in orbit or in transit and in extremely dusty environments at destinations such as the moon and Mars. Historically, oil development was guided by terrestrial application, which did not provide sufficient space lubricants. Novel fluids such as perfluorinated polyethers provided some relief but are far from ideal. With each new fluid proposed to solve one problem, other problems have arisen. Much of the work performed at National Aeronautics and Space Adminstration's (NASA) Glenn Research Center, in elucidating mechanisms by which chemical degradation of space oils occur, has been done by infrared and Raman microspectroscopy, which this review details. Fundamental lubrication studies are presented as well as actual case studies, in which vibrational spectroscopy led to millions of dollars in savings and potentially prevented loss of mission.     

二羰基茂铁二聚体[CpFe(CO)2]2的中红外泵浦探测光谱

利用一维稳态红外光谱和5-μm泵浦探测红外光谱手段,结合量子化学计算,以非桥连三价羰基为探针,研究了二羰基茂铁二聚体[CpFe(CO)2]2在二氯甲烷中的结构和振动动力学.结果表明,[CpFe(CO)2]2两个主要结构(顺式cis和反式trans摩尔比为1.7)的振动态寿命和转动动力学都有一定不同.两种结构的两个羰基振动激发态的指数衰减过程都有一个<1ps的快组分和一个~20ps的慢组分.我们认为前者与宽带激发所产生的振动相干态的快速失相过程有关,而后者属于典型的C≡O伸缩振动态寿命.此外,cis结构与溶剂的较强作用使得其转动衰减较慢.结果表明,非桥连羰基的红外吸收频率和振转动力学对分子结构和溶剂环境都非常敏感.     

丙氨酸二肽分子二级结构与振动光谱特性

利用从头算方法探索蛋白质模型分子——丙氨酸二肽的二级结构布居特性以及体系势能变化. 引入对分子结构敏感的振动探针(酰胺振动吸收带), 借助其光谱表象, 寻求振动光谱参数与分子结构之间的联系. 研究结果表明: 丙氨酸二肽分子处于C_7eq构型(Φ/Ψ=-80°/80°)时具有最低能量值, 且分子易形成β折叠、PP_II、C₅及C₇等能量较低的稳定构型. 通过简正模式分析, 得到分子3N-6 个振动模式的吸收光谱, 并通过势能分布分析方法对分子骨架上酰胺振动吸收带的特征振动模式进行了指认. 重点考察分子骨架上酰胺-I带振动光谱参数与分子构型变化之间的相关性, 建立振动光谱参数与蛋白质二级结构之间的联系, 为在化学键水平上研究蛋白质的结构及其发挥作用的机制提供科学依据.     

High frequency acoustic attenuation of vitreous silica: New insight from inelastic x-ray scattering

We present new experimental results on the propagation and damping of the high frequency acoustic-like modes in vitreous silica. The new data are measured by means of the inelastic x-ray scattering technique down to an exchanged wavevector Q ∼ 0.9 nm ^− 1, at the limit of the instrument capabilities. Thanks to the continuous development of the technique, the new spectra are characterized by a very high signal to noise ratio when compared to previous experiments. The higher data quality finally allows for a reliable determination of the position and width of the inelastic excitations. The new data show that the sound damping Γ is marked by a frequency dependence compatible with the Rayleigh law, Γ ∼ ν⁴, for frequencies below the position of the excess vibrational modes at the boson peak. We show that the new data are in good agreement with estimates of the acoustic mean free path from the thermal conductivity, which take into account the peculiar plateau at a few Kelvin. The connection between the boson peak and the Rayleigh law is further confirmed by a comparison of the present data with literature data for the sound attenuation in a permanently densified silica sample.     

基态SiH~+分子离子光谱常数与振动能级研究

首先根据群论及原子分子反应静力学的相关知识,推导了SiH+分子离子基态X1Σ+的电子态和合理的离解极限。然后采用Gaussian 09程序包中优选出的QCISD(T)方法结合cc-pVQZ基组,对SiH+分子离子基态结构进行了优化计算。运用相同方法对SiH+分子离子基态进行了单点势能扫描,分别采用9参数Murrell-Sorbie函数及Murrell-Sorbie+c6函数进行了非线性最小二乘拟合,首次得到了SiH+分子离子基态的势能函数和相应的光谱常数ωe,ωexe,Be,αe。计算结果表明,利用9参数Murrell-Sorbie函数计算所得的光谱常数与实验光谱数据吻合得更好,相对误差分别为0.13%,3.07%,0.38%,5.25%以及0.52%,这些数据均说明9参数Murrell-Sorbie势能函数能更好地描述SiH+分子离子基态的性质,拟合所得势能曲线准确地再现了其离解能和平衡结构特征。通过求解双原子分子核运动的径向薛定谔方程,首次报道了SiH+分子离子基态在J=0时的振动能级、转动惯量和六个离心畸变常数。为实验上找到对应的跃迁提供了理论依据。