无机-有机杂化非线性光学晶体材料LAP和d-LAP晶体红外吸收边计算

根据双原子谐振子模型近似,提出了估算分子晶体材料红外吸收边的理论方法,然后利用超分子量子化学从头算,计算了L-精氨酸一水磷酸盐(LAP)晶体和氘化L-精氨酸一水磷酸盐(d-LAP)晶体单元超分子的红外振动光谱,其中LAP晶体超分子计算值与晶体红外光谱实验值吻合,表明超分子计算能有效地模拟无机-有机杂化非线性光学晶体的红外振动光谱。在归属了超分子重要基频线后,分析其红外强度,并估算了泛频频率。根据我们提出的方法,估算了这两种晶体的红外吸收边,结果与实验值较吻合。表明我们建议的理论方法是合理的。此外,通过计算表明,如果非线性光学晶体材料的红外吸收边是由与活泼H有关的伸缩振动泛频频率决定,那么活泼H的氘化是一种改善红外吸收边的有效途径。     

尿素分子红外光谱与晶体红外吸收截止波长的量子化学研究

应用量子化学从头算方法准确计算了尿素分子的红外光谱,得到分子的振动频率和红外振动强度与实验值相符。在分子红外光谱计算的结果基础上估算了尿素晶体的红外吸收截止波长,其值为１．４０μｍ,与测量的符合得很好。对光学晶体红外透过窗口的研究具有重要意义。     

DL-丙氨酸晶体粉末的拉曼光谱研究

拉曼光谱可作为研究分子晶体中分子振动和晶格振动的重要手段.DL-丙氨酸晶体和L-丙氨酸晶体晶胞参数相近,结构上同属于正交晶系,但它们的空间群不同,L-丙氨酸晶体的空间群是P212121,而DL-丙氨酸晶体则是Pna21.前人的工作详细研究了L-丙氨酸晶体的拉曼光谱.文章通过对DL-丙氨酸晶体粉末的拉曼光谱研究,和相同条件下D-和L-丙氨酸晶体粉末的拉曼光谱比较,获得了有关DL-丙氨酸晶体中氢键作用和分子构象的信息.     

高温下季戊四醇晶体的结构和振动性质的分子动力学模拟

通过分子动力学研究了季戊四醇晶体在温度高达500K范围内的结构和振动性质。考察了季戊四醇晶体的晶格参数和分子构型等随温度变化情况,相对晶格常数a来说,晶格常数c容易被压缩。发现C-C,C-H和 C-O键随温度的变化较大,这意味着在分解过程中这些键可能较敏感,即最先断裂可能性较大。研究了季戊四醇晶体在不同温度下的振动,在常压下,我们所计算的振动频率高于实验结果,另外,我们还讨论了由温度引起的频率漂移。     

高温下季戊四醇晶体的结构和振动性质的分子动力学模拟(英文)

通过分子动力学研究了季戊四醇晶体在温度高达500K范围内的结构和振动性质.考察了季戊四醇晶体的晶格参数和分子构型等随温度变化情况,相对晶格常数a来说,晶格常数c容易被压缩.发现C-C,C-H和C-O键随温度的变化较大,这意味着在分解过程中这些键可能较敏感,即最先断裂可能性较大.研究了季戊四醇晶体在不同温度下的振动,发现大部分频率随温度的升高而降低.     

分子振动全分析方法和程序

本文从一般价力场的Wilson-GF矩阵法出发,提出分子和晶体振动简正坐标特征标封闭公式、线型分子振动简正坐标与内坐标对称性种类公式及一种新的快速的、可避免力常数振荡、发散和相关困难的力常数调整方法──对称循环逼近法(SCAM),并在此基础上用BASICA语言编写了《分子振动全分析程序(MVTA)》。实践表明:MVTA可十分有效地用于分子振动分析全过程。     

低温相H_2S晶体振动光谱计算

本文介绍了计算分子晶体基频振动的力常数模型并应用于Ｈ２Ｓ晶体低温相的拉曼，红外光谱分析。使用１１个可调参数（包括３个分子内部力常数和８个分子间作用力参数）计算得到６９个光学模式的振动频率及其对应的本征矢量。计算结果与实验值相符甚好。对已观测到的谱线作了全面指认。并给出了未观测到谱线的位置。计算表明，晶体中氢键为最重要的分子间相互作用。它使Ｈ２Ｓ分子Ｓ—Ｈ键力在晶体中减弱７％。     

除虫脲和高效氯氟氰菊酯的太赫兹光谱及密度泛函理论研究(英文)

利用太赫兹时域光谱技术及密度泛函理论对两种常用的卫生杀虫剂除虫脲和高效氯氟氰菊酯的低频振动光谱进行了研究。室温下观测到两种物质在0.2～2.2THz内的实验谱分别有5和7个吸收峰,可作为其在THz波段的指纹谱用于分子识别。为了深入理解太赫兹吸收峰的振动特性,我们采用Gaussi-an03和CRYSTAL09软件分别进行了单分子和晶体的密度泛函理论模拟。晶体模拟结果预测出两种物质在0.2～2.2THz实验谱中所有的吸收峰,明显优于单分子模拟结果。最后通过晶体密度泛函理论模拟的简正模式分析获得不同吸收峰处的振动模式归属。结果证明太赫兹光谱技术在农药分子识别以及晶体密度泛函理论模拟在太赫兹吸收峰指认和振动模式归属方面的可行性。     

固体的光散射讲座第三讲 晶格振动的喇曼散射

晶体的喇曼散射是研究晶体内部结构的一种简单而有效的成熟方法.它对研究材料的结构和结构相变以及各种特殊条件下的晶体状态有着重要的作用.本文先从晶体的对称性出发,讨论晶格振动的分类,并以k=0处的晶格振动为例,介绍晶格振动模的对称类的分类.然后简述晶体喇曼散射的机理以及对晶体喇曼谱的实验研究. 一、晶体的对称性 我们知道,分子具有一定的点对称性,即保持体系中一点位置不变,对体系施以转动、反射或反演等(点)对称操作,体系仍处于与操作前等效的状态.晶体不仅也具有这种点对称性,而且由于其中原子排列的周期性,晶体还具有平移对称…     

偏硼酸钡晶体晶格振动的群论分析与喇曼光谱

本文对新型紫外倍频晶体偏硼酸钡(β-BaB_2O_4)的晶格振动进行了群论分析。该晶体的空间群为C_3~4(R3)。用位置对称性方法对它的振动模的对称性进行分类,得到:P=126A+126E,全部振动模均为极性晶格振动模。我们还计算了各种几何配置下晶体的喇曼散射效率。同时,本工作首次获得偏硼酸钡晶体在各种不同几何配置下的喇曼散射光谱。运用群论分析的结果,利用“层状分子性结构”模型,对谱图出给了初步识别。     

Vibrational chaotic dynamics in triatomic molecules: A comparative study

Within Lie algebraic model, the vibrational chaotic dynamics in triatomic molecules are studied. The molecules of H₂S, NO₂, and O₃ are sampled to explore the dynamical differences between the local and normal mode molecules. The comprehensive effects of the local and normal mode vibrations, resonances and chaos on the dynamical entanglement are studied. The results demonstrate that the resonances as well as chaos can promote the evolution of dynamical entanglement.     

A molecular dynamics investigation of dynamical heterogeneity in supercooled water

We investigate the presence of dynamical heterogeneity in supercooled water with molecular dynamics simulations using the new water model proposed by Mahoney and Jorgensen [M.W. Mahoney, W.L. Jorgensen J. Chem. Phys. 112, 8910 (2000)]. Prompted by recent theoretical results [J.P. Garrahan, D. Chandler, Phys. Rev. Lett. 89, 35704 (2002)] we study the dynamical aggregation of the least and the most mobile molecules. We find dynamical heterogeneity in supercooled water and string-like dynamics for the most mobile molecules. We also find the dynamical aggregation of the least mobile molecules. The two kinds of dynamical aggregation appear however to be very different. Characteristic times are different and evolve differently. String-like motions appear only for the most mobile molecules, a result predicted by the facilitation theory. The aggregation of the least mobile molecules is more organized than the bulk while the opposite is observed for the most mobile molecules.     

非链式脉冲DF化学激光器反应动力学模型

依据非链式脉冲氟化氘(DF)激光器的反应机理, 采用速率方程理论, 综合考虑了基态DF分子、D₂分子、D原子、F原子对激发态DF分子的消激发作用, 建立了非链式脉冲DF激光器反应动力学模型. 运用Runge-Kutta法对该模型进行数值计算, 得到了增益区内各组分粒子数密度随时间的变化关系. 进而运用该模型研究了工作气体配比和输出镜反射率对DF激光器腔内光子数密度、 单脉冲能量、脉冲宽度和输出功率的影响, 得到了最佳气体配比和最佳输出镜反射率参数. 采用放电引发方式对非链式DF激光器进行了实验研究, 实验测得脉冲波形及单脉冲能量与速率方程理论模型计算结果基本一致. 本文的研究结果可为非链式脉冲DF激光器的优化设计提供理论参考. 关键词： 脉冲DF激光器 动力学模型 速率方程 数值计算     

Exact solution of the asymmetric exclusion model with particles of arbitrary size

A generalization of the simple exclusion asymmetric model is introduced. In this model an arbitrary mixture of molecules with distinct sizes s=0,1,2, ..., in units of lattice space, diffuses asymmetrically on the lattice. A related surface growth model is also presented. Variations of the distribution of the molecules sizes may change the excluded volume almost continuously. We solve the model exactly through the Bethe ansatz and the dynamical critical exponent z is calculated from the finite-size corrections of the mass gap of the related quantum chain. Our results show that for an arbitrary distribution of molecules, the dynamical critical behavior is on the Kardar-Parizi-Zhang universality.     

Theoretical study of slowing supersonic CH3F molecular beams using electrostatic Stark decelerator

We have calculated the Stark effect of CH3F molecules in external electrical fields,the rotational population of supersonic CH3F molecules in different quantum states,and analyse the motion of weak-field-seeking CH3F molecules in a state |J = 1,KM = 1 inside the electrical field of a Stark decelerator by using a simple analytical model.Threedimensional Monte Carlo simulation is performed to simulate the dynamical slowing process of molecules through the decelerator,and the results are compared with those obtained from the analytical model,including the phase stability,slowing efficiency as well as the translational temperature of the slowed molecular packet.Our study shows that with a modest dipole moment(～1.85 Debye) and a relatively slight molecular weight(～34.03),CH3F molecules in a state |J = 1,KM = 1 are a good candidate for slowing with electrostatic field.With high voltages of ±10 kV applied on the decelerator,molecules of 370 m/s can be brought to a standstill within 200 slowing stages.     

Direct observation of H2 binding to a metal oxide surface

Inelastic neutron scattering is used to probe the dynamical response of H2 films adsorbed on MgO(100) as a function of film thickness. Concomitant diffraction measurements and a reduced-dimensionality quantum dynamical model provide insight into the molecule-surface interaction potential. At monolayer thickness, the rotational motion is strongly influenced by the surface, so that the molecules behave like quasiplanar rotors. These findings have a direct impact on understanding how molecular hydrogen binds to the surface of materials used in catalytic and storage applications.     

Neutron,x-ray and lattice dynamical studies of paraelectric Sb2S3

Neutron and x-ray diffraction studies of Sb₂S₃ indicate extensive diffuse scattering in the plane perpendicular to the chain axis of polymer-like (Sb₄S₆) _n molecules. The crystal structure of the paraelectric phase is said to be orthorhombic with space group D _2h ¹⁶ with four molecules per unit cell. The observed diffuse scattering may be due to static disorder or some dynamical effects. In this paper the authors have examined the possible dynamical origin by recourse to lattice dynamical studies. Dispersion relation of phonons along the three symmetry directionsa*,b* andc* is evaluated based on a lattice dynamical model incorporating Coulomb, covalent and a Born-Mayer-like short range interactions. Group theoretical analysis based on the group of neutral elements of crystal sites (GNES) was essential in order to examine and aid in the numerical computations. The group theoretical technique involving GNES extended to ‘pseudo-molecular’ systems is also discussed in this context. The phonon dispersion relation shows that there are rather flat TA-TO branches of very low frequency in thea andc directions which may give rise to diffuse scattering. The branches along theb-axis are quite dissimilar to those alonga andc axes because of anisotropy. Variation of the potential parameters leads to instability of the lowest TA-TO branch. This is suggestive of a temperatures or pressure-dependent phase transition. However since these modes are optically ‘silent’ one needs to carry out either high resolution neutron scattering or ultrasonic studies to confirm various aspects of the theoretical studies.     

Dynamical aspects of two-molecule collision process in a diatomic gasdynamic laser

A dynamical analysis on the basic collision process between two molecules is presented within the context of diatomic gasdynamic lasers. In particular, the kinetic energy of the colliding molecules resulting from the process above is considered for quite highly excited bound states from a quasi-classical point of view. In this analysis, the magnitude of molecule velocity is calculated and discussed in terms of the anharmonicity of a given molecule as a quantum anharmonic oscillator.     

Collective molecule formation in a degenerate Fermi gas via a Feshbach resonance

We model collisionless collective conversion of a degenerate Fermi gas of atoms into bosonic molecules via a Feshbach resonance, treating the bosonic molecules as a classical field and seeding the pairing amplitudes with random phases. A dynamical instability of the Fermi sea against association with molecules drives the conversion. The model qualitatively reproduces several experimental observations [Regal et al., Nature (London), (2003)]. We predict that the initial temperature of the Fermi gas sets the limit for the efficiency of atom-molecule conversion.