基态MgB2分子的结构与分析势能函数

应用群论及原子分子反应静力学方法推导MgB₂分子的电子状态及其离解极限,采用密度泛函B3LYP和从头计算QCISD方法在6-311++G**基组水平上,对MgB₂分子可能的状态进行优化计算,得出MgB₂的三重态能量最低,其稳定构型为C_2v,平衡核间距R_e=2.2977,键角α_BMgB=41.5521°,能量为-248.9645a.u.同时还计算了基态的简正振动频率:对称伸缩振动频率ν（B₂）=315.4430 cm^-1,反对称伸缩振动频率ν（A₁）=418.1883 cm^-1和弯曲振动频率ν（A₁）=968.9672 cm^-1.在此基础上,使用多体项展式理论方法,导出了基态MgB₂分子的解析势能函数,其等势面准确再现了基态MgB₂平衡结构和离解能,并由此讨论了B+MgB和Mg+BB分子反应的势能面静态特征. 关键词： 2')" href="#">MgB₂ 多体项展式理论 解析势能函数     

高温快速固相烧结合成Zr1-xHfxW2O8的Raman光谱研究

首次采用高温快速固相烧结的方法合成了Zr1-x Hfx W2O8(x=0, 0.2, 0.3, 0.4, 0.5, 0.6, 1)固溶体。合适的合成条件为: 温度1573~1693 K, 时间10 min~1 h, 该方法使合成时间和能耗比传统固相反应烧结显著降低。Zr1-x Hfx W2O8的晶胞参数与晶胞体积随Hf4+含量的增加而减小。合成的样品晶粒尺寸比常规固相烧结合成样品的颗粒尺寸较小, 颗粒大小在1～10 μm之间。拉曼光谱分析表明, Zr1-xHfxW2O8(0相似文献   

Extreme tunnelling in methylamine dehydrogenase revealed by hybrid QM/MM calculations: potential energy surface profile for methylamine and ethanolamine substrates and kinetic isotope effect values

The rate-determining proton transfer step in the amine reduction reaction catalysed by the enzyme methylamine dehydrogenase has been studied using a hybrid quantum mechanical/molecular mechanical (QM/MM) model. Variational transition state theory, combined with multidimensional tunnelling corrections, has been employed to calculate reaction rate constants, and hence deuterium kinetic isotope effects (KIE). To render these calculations computationally feasible, the electronic structure was described using a PM3 method with specific reaction parameters obtained by a fit to energetics obtained at a high level for a small model system. Compared to the use of standard parameters, these revised parameters result in a considerable improvement in the predicted KIE values and activation energy. For both methylamine and ethanolamine substrates, through-barrier, rather than over-barrier, motion is found to dominate with KIE values that are large and close to the experimental values. A major difference between the two substrates is that, for ethanolamine, different hydrogen bonding structures involving the substrate hydroxyl are possible, leading to very different potential energy surfaces with KIE values covering a considerable range. We speculate that this is the origin of the differing temperature behaviour observed for the KIEs of the two substrates.     

THE MASSIVE TRANSFER IN 12C+197Au REACTION

In this paper, we present energy spectra and angular distributions for the α-par-ticles emitted in the reaction of ¹²C+¹⁹⁷Au at 64 and 67 MeV and for α, Be and B emittedin the reaction at 71.5 MeV. The most-probable energles of the variousproducts emittedin this reaction decrease.with decreasing incident energy. The angular distributions peak near grazing angle.The peak position of the angular distributions shift from--80°to--120°while the projec-tile energy decreases from 71.5 MeV to 64 MeV. These all show the features of the transferreaction. The ⁶Li product also has been measured and the ⁸Be particle emitted from thisreaction was detected at 90°to the beam direction using α-α coincident technique at 71.5MeV. The coross section of the ³Be is only few percent at the same angle.     

碰撞反应Ca+C2H5Br和Ca+nC3H7Br产物CaBr的内能态分布

采用准经典轨线方法研究了碰撞反应Ca+C2H5Br和Ca+nC3H7Br产物CaBr的内能态分布,计算了产物分子CaBr的平均振动、转动和平动能量以及总可资用能量.结果表明,当碰撞能为7.54kJ/mol时,产物的能量主要为振动能量;随着碰撞能增加,产物的平动能和转动能增加,而振动能略微减小,最可几振动态向较低振动能级移动;反应物分子内能态分布对产物分子的内能态分布影响很小;反应基团越大,产物的振动能占总可资用能量的比例就越高.碰撞反应Ca+C2H5Br和Ca+nC3H7Br均存在两条竞争的反应路径迁移相碰和直接反应路径.前者产生高振动激发态产物CaBr,后者引起C-Br键断裂.当碰撞能增加时,两种反应均倾向于后者.     

Raman study on the pressure-induced disordered state of polystyrene

The pressure-induced disordered state was first reported for iPS, the polymer showing thermal shrinkage. The low-frequency Raman study showed clearly that pressure introduces irregularity into the polymer backbone of iPS. It has also been revealed that there exist two types of vibrational modes, which show different sensitivities on the regularity of the main chain. These modes indicate two distinctive features of dispersion in the ordered form. In the disordered state, the dispersive modes smear out and the dispersionless one survives to be observed. We conclude that pressure causes the ordered-disordered conversion like thermal shrinkage. This conversion will be a common feature of the polymers showing thermal shrinkage and would be able to take place at relatively low pressure.     

Reaction pathway and H/D kinetic isotope effects of the triple proton transfer in a 7‐hydroxyquinoline‐methanol complex in the ground state: A computational approach

Multiple proton transfer (PT) is an essential process in long‐range proton transport such as proton relay in enzymes. 7‐Hydroxyquinoline (7HQ) undergoes alcohol‐mediated PT in both the excited and ground states, and this system has been investigated as a biomimetic model. In the present study, the reaction pathway of triple PT in a 7HQ‐methanol cluster, 7HQ·(MeOH)₂, in the ground state has been investigated using density functional theory calculations to clarify the reaction mechanism and the origin of the experimentally observed kinetic isotope effect (KIE). The PT takes place in an asynchronous concerted fashion, in which the oxygen atom in 7HQ first accepts a proton from the directly hydrogen‐bonded MeOH. The rate constants and primary H/D KIEs have been estimated with canonical variational transition state theory in combination with the small curvature tunneling approximation. The tunneling effect on the PT rate is significant, and the KIE is much greater than 1 at room temperature. The rule of the geometric mean for the KIEs breaks down because of the asynchronicity in the motions of 3 protons and tunneling effect. In addition, the rate constant is smaller, the KIE is larger, and the activation energy is higher compared with the experimental values in heptane solution, suggesting that the PT dynamics in solution is governed by not only the intrinsic PT process but also thermal fluctuation of the solute and solvent molecules, which plays an important role in the configurational change of the 7HQ·(MeOH)₂ complex.     

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(X1∑+,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(x1∑+)分子,探测激光延迟泵浦激光20 ns,通过激光感应荧光光谱(LIF)的测量,确定了X1∑+(v=0～2,J)原生态的转动...     

倾斜式生长ZnS纳米柱状薄膜及其透射性能的研究

采用倾斜式生长的方法,在本底真空为3×10-4 Pa,生长率为0.2 nm·s-1的条件下,通过改变衬底的法线方向与入射粒子流的夹角α,在ITO导电玻璃衬底上制备了ZnS纳米薄膜。在α=80°和85°时,样品的Ｘ射线衍射谱证实了不同倾斜角时所制备薄膜中均有纳米ZnS晶体形成,扫描电子显微镜(SEM)图像显示,所形成的薄膜均呈现出了柱状结构,并且倾斜角为85°时所得到的纳米柱直径大于80°时所得结果;在α=0°时,相应测量结果表明,虽然在不同衬底上也形成了纳米ZnS晶体薄膜,但并未见柱状结构,而是形成了一层均匀且致密的薄膜。对两种薄膜结构的生长动力学过程作了分析。ITO衬底上薄膜的透射光谱表明ZnS柱状薄膜能够提高可见光的透过率,因此对柱状ZnS纳米薄膜的研究将有利于提高电致发光器件的发光效率。     

Vibrational properties of RbNd(WO4)2: high pressure Raman study, structural and phonon calculations

RbNd(WO(4))(2) was investigated by high pressure Raman spectroscopy in the 0.1-12.3 GPa pressure interval. The assignment of modes was made based on lattice dynamics calculations and the results of these calculations helped us to also discuss the high pressure behavior of phonon spectra in this material. Our results show that a double oxygen bridge plays a fundamental role in the vibrational properties of this system. A density functional theory (DFT) calculation of hydrostatic pressure effects on RbNd(WO(4))(2) was performed in order to understand the effect of internal bond changes on the vibrational properties of RbNd(WO(4))(2). No pressure induced structural phase transition was observed in the Raman study at room temperature, and the DFT calculation (T = 0 K) is consistent with this result. The anomalous softening of the bridge stretching mode at 770 cm(-1) was attributed to the decrease of W-O1-W bond angle with increasing pressure.     

高温高压下草酸脱羧反应中的拉曼光谱研究

应用水热金刚石压腔结合拉曼光谱技术研究了高温高压下草酸溶液的热稳定,使用拉曼光谱对其脱羧反应及产物进行监测。结果表明低温升温过程中,草酸的拉曼谱图中各个特征振动峰没有发生变化,随着温度的继续升高,其特征振动峰逐渐变弱。达到一定温度后,羧基的拉曼特征峰消失,草酸发生脱羧反应:C2H2O4—2CO2+H2生成CO2和H2。高温高压下草酸发生热分解的温度压力之间呈线性关系,其线性回归方程为P(MPa)=12.839 T(K)-5 953.7,R2=0.99。草酸脱羧反应的摩尔体积变化与温度压力的关系为ΔV(cm-3.mol-1)=16.69-0.002P(MPa)+0.005 2T(K),R2=0.99。     

还原态烟酰胺腺嘌呤二核苷酸拉曼光谱研究

还原态烟酰胺腺嘌呤二核苷酸(NADH)在维持细胞生长、分化、能量代谢以及细胞保护方面起着非常重要的作用,NADH的无创在体检测具有非常重要的意义。运用激光拉曼散射实验和密度泛函理论(DFT)计算研究了200～3 300 cm-1光谱范围内NADH分子的振动模式特性。DFT计算采用了B3LYP杂化方法,并选用了极化6-311+G(d,p)基组。为了准确的分析NADH分子的振动模式和频率,首先运用B3LYP/6-311+G(d,p)理论对NADH分子的基态结构进行了几何优化,并计算了基态结构NADH分子的各个键长和键角。同时考虑到DFT计算中的非谐性,运用波数线性标度方法对所有计算所得振动模式波数重新进行了标度。重新标度后,DFT计算所得的振动模式波数与激光拉曼散射实验观测到的拉曼峰波数吻合的很好：在200～3 300 cm-1整个光谱范围内,计算与实验结果具有非常好的线性相关性,而且大部分振动模式的计算与实验之间的偏差都小于5 cm-1。此外,讨论了实验观察所得拉曼光谱的分子振动模式归属,分析了NADH分子中腺嘌呤、烟酰胺、及二核苷酸的特征振动模式,并初步提出了运用拉曼光谱实现NADH快速准确无创在体检测的方法。位于732 cm-1处的拉曼峰是腺嘌呤的特征振动模式,而且可以选为检测NADH分子的最特征拉曼峰。位于1 690 cm-1处的拉曼峰是烟酰胺的特征振动模式,可以选为进一步准确检测NADH分子的另一个特征拉曼峰。位于1 086和1 339 cm-1两处拉曼峰的组合可以作为二核苷酸的特征振动模式,用于进一步更准确的检测NADH分子。所以在运用拉曼光谱法实现NADH快速准确无创在体检测时,可以首先运用位于732 cm-1处NADH分子的最特征振动模式进行快速检测,然后再运用位于1 690 cm-1及1 086和1 339 cm-1组合等特征振动模式进行准确分析。     

A study of the reactivity of silver azide based on calculations of the band properties within the framework of density functional theory

Density functional theory methods in the basis of localized orbitals are used to study structural, electronic, vibrational, and thermodynamic properties, as well as the reactivity of the orthorhombic, tetragonal, and monoclinic phases of silver azide. The effects of pressure and temperature are described using the Debye quasi-harmonic model. The reactivity of silver azide is analyzed in terms of the enthalpy and entropy factors and equilibrium constants. It is shown that, for the solid-phase decomposition, a decrease in the volume (increase in pressure) leads to a decrease in the enthalpy, whereas the entropy factor remains virtually unchanged. As a result, at a pressure of 11.6 GPa, the reaction of direct generation of holes becomes feasible and then, above 14.8 GPa, exothermic. The formation of small nuclei of silver dinitride-nitride AgNN₂ metastable phase is considered as a possible mechanism of generation of reaction kernels.     

NO2分子在550～740 nm范围内的激光诱导荧光光谱

以皮秒Nd：YAG激光器的二倍频输出(532nm)作为激发源,在室温下,对NO2分子在低气压和较高气压情况下进行了激光诱导荧光研究。在低气压条件下获得了在550～740nm范围内的振动序列,将其归属为由第一电子激发态A^2B2态向基电子态X^2A1态不同振动态的跃迁,由此得到对称振动模式和弯曲振动模式的谐振频率,分别为ω1=1300．72cm^-1和ω2=744．14cm^-1.并在此基础上对较高气压下荧光光谱产生的明显红移现象进行了解释,得到了有意义的结果。     

PdY合金及其一氢化物分子结构及热力学函数的研究

本文利用B3LYP的密度泛函方法对PdY、 PdYH的分子结构进行了优化,得到PdY最稳定的电子态为2∑,RPdY=0.2418 nm,ωe=249.66cm-1,De=2.75eV.PdYH最稳定构型为Cs,1A'态,RPdY=0.243 0 nm,RYH=0.197 4nm,∠PdYH=116.54°,谐振频率v1(a')=1 450.83cm-1,v2(a')=351.21cm-1,v3(a')=243.71cm-1,离解能De(PdYH)为5.64 eV.并以气态分子总能量中的振动能Ev代替分子处于固态时的振动能,以电子运动和振动运动熵SEv代替分子处于固态的熵的近似方法计算了PdY与氢及其同位素反应的△Hθ、△Sθ、△Gθ及氢化反应平衡压力,得出PdYH(S)的生成焓为60.32kJ·mol-1.     

A stable superconducting state at 8 K and ambient pressure in\alpha _t - (BEDT - TTF^ \star )_2 I_3 ^1

We report bulk superconductivity at 8 K and ambient pressure in crystals of α _t (BEDT-TTF)₂I₃. In contrast to the earlier observed metastable superconducting state at 8 K in crystals of β-(BEDT-TTF)₂I₃ here the superconducting state is stable and the crystals can be prepared by tempering α-(BEDT-TTF)₂I₃ above 70 °C for several days. ac-susceptibility measurements show that the observed superconducting state at 8 K is a bulk property of the crystals. Resistivity measurements indicate a sharp superconducting transition at 8 K with an onset temperature of about 9 K. The upper critical fields H_c2 at 1.3 K lie between 3 and 11 T depending on the direction of the magnetic field with respect to the crystal axes. ESR- as well as NMR-measurements indicate a total transformation of the α-phase crystals into the new superconducting α _t -crystals after tempering.     

Cl+CHD3(v1=1)反应中的成对动态学:侦测激光波长的效应

用交叉分子束试验探讨氯原子与C?H 键激发的CHD3化学反应，并用(2+1)共振多光子电离及离子影像法来侦测CD3基态生成物．发现所得的影像对电离光子的波长极为敏感．这表明，与基态反应比较，C?H激发反应较易产生转动激发的CD3．实验结果也证明CD3D的转动与HCl的振动激发有相反的关联性．     

Ni+与CH3CH2CH2NH2反应机理的理论研究

用密度泛函方法在UB3LYP/6-311G++(d,p)理论水平上研究了Ni+在基态与CH3CH2CH2NH2的反应机理,全参数优化了[Ni,C3,N,H9]+基态势能面上各驻点的几何构型,并用频率分析方法和内禀反应坐标（IRC）方法对过渡态进行了验证。结果表明第一过渡金属离子Ni+与CH3CH2CH2NH2的反应为插入-消去机理,并计算找到了基态下该反应的最有利通道。     

Scanning the energy dissipation process of energetic materials based on excited state relaxation and vibration–vibration coupling

The energy dissipation mechanism of energetic materials(EMs) is very important for keeping safety. We choose nitrobenzene as a model of EM and employ transient absorption(TA) spectroscopy and time-resolved coherent anti-stokes Raman scattering(CARS) to clarify its energy dissipation mechanism. The TA data confirms that the excited nitrobenzene spends about 16 ps finishing the twist intramolecular charge transfer from benzene to nitro group, and dissipates its energy through the rapid vibration relaxation in the initial excited state. And then the dynamics of vibrational modes(VMs) in the ground state of nitrobenzene, which are located at 682 cm~(-1)(v_1), 854 cm~(-1)(v_2), 1006 cm~(-1)(v_3), and 1023 cm~(-1)(v_4),is scanned by CARS. It exhibits that the excess energy of nitrobenzene on the ground state would further dissipate through intramolecular vibrational redistribution based on the vibrational cooling of vi and v_2 modes, v_1 and v_4 modes, and v_3 and v_4 modes. Moreover, the vibration-vibration coupling depends not only on the energy levels of VMs, but also on the spatial position of chemical bonds relative to the VM.     

Reaction dynamics of Cl O ClO O

Applying the two photon laser induced fluorescence technique for nascent state resolved ClO() detection, the reaction dynamics of Cl+O ClO+O₂ is investigated. The ClO product is formed in its electronic ground state ClO(). A complete product state analysis in terms of vibration, rotation, spin-orbit and -states indicates that nascent ClO radicals are formed in v =0-6 vibrational states peaking at v =3. The ClO fragment shows a moderate rotational excitation, described by a Boltzmann distribution with a temperature parameter of 1300 K 200 K. The spin orbit ratio of :. Most of the excess energy is released as translational energy or as internal energy of the O₂ product. By comparing our results with the trajectory studies of Farantos and Murrell, we favour a reaction mechanism, where the transition complex is planar containing an essentially linear OOCl group. In order to determine the possible influence of vibrationally excited ClO on other trace components of the atmosphere, especially the reaction ClO(v >0)+ O₃, a rough estimate of the vibrational relaxation rate of ClO with the major atmospheric collision partner, N₂, has been performed. A measurement of the vibrational distribution of ClO at different N₂ pressures indicates a mean vibrational relaxation rate of . Received: 27 February 1998 / Revised: 1st April 1998 / Accepted: 15 April 1998