氨基酸分子的光学活性和频效应

用带限制场Hartree-Fock (RHF/6-311++G^**)从头算的方法进行分子构型优化, 单激发态组态相互作用(CIS/6-311++G^**)计算各种需要的相关数据; 应用态求和理论, 以长度偶极矩和速度偶极矩两种形式模拟了一系列氨基酸离子的光学活性和频效应(OA-SFG)光谱. 结果表明速度偶极矩计算得到的一系列氨基酸离子的和频效应光谱强度顺序能很好地与实验相吻合, 而长度偶极矩形式计算得到的结果与实验不吻合. 引起这两种形式和频效应光谱理论计算结果差别的原因是由于长度偶极矩形式具有原点敏感性, 而速度偶极矩没有. 速度偶极矩方法更适用于分子光学活性和频效应的模拟.     

白藜芦醇分子的转动惯量和电偶极矩

通过分子轨道理论和杂化轨道理论推断出较稳定的白藜芦醇分子是平面型分子,然后根据白藜芦醇分子结构特点计算了该化合物的一种稳定异构体的转动惯量,用矢量合成法计算了其电偶极矩,为微波辅助白藜芦醇萃取理论研究提供转动惯量和电偶极矩的数据.     

极性分子键角与键偶极矩的关系

研究了基态极性分子的键角和键偶极矩之间的关系。我们采用原子偶极矩校正的Hirshfeld （ADCH）电荷来计算键偶极矩,利用电子的局域函数和键临界点处的局域函数值来分析键的电子结构。通过对IVA族（IVA = C,Si,Ge）、VA族（VA = N,P,As ）、VIA族（VIA = O,S,Se）和VIIA族（VIIA = F,Cl,Br）元素形成的系列共价型基态分子,以及环状基态分子的键角和键偶极矩数据进行分析,发现在键的电子结构类似的情况下,由于键偶极矩的排斥作用,这些分子的键角随键偶极矩的增加而增大。这一发现有助于加深我们对分子几何结构的认识。     

星际尘埃HC_(3-x)NC_x(x=0～3)与HC_(5-x)NC_x(x=0～5)分子的DFT研究

运用密度泛函理论（DFT）中的B3LYP方法,计算了星际尘埃HC_3N,HC_5N分子 及它们的同分异构体的分子结构、相对稳定性、偶极矩、转动常数等,对于HC_(3- x)NC_x(x = 0～3),HC_3N分子比其它的异构体要稳定,将计算所得的HC_3N, HC_2NC的转动常数B_0与实际的观测值B_0相比较,发现两者能较好地吻合。比较 HC_(5-x)NC_x(x = 0～5)的各同分异构体的总能量,发现HC_5N的相对稳定性最高 ,但它的偶极矩相对较低。将HC_5N的转动常数B_0的理论计算值与实际观测值进行 比较,其相对标准误差仅0.6%。     

标准差标准化方法修正的PBBs多效应3D-QSAR模型及其在环境友好性分子修饰中的应用

构建了标准差标准化方法修正的兼具多溴联苯(PBBs)分子红外振动强度、 生物富集性和毒性3种效应的CoMFA模型, 分析了PBBs分子力场对其综合值的影响, 确定取代位点, 并进行兼具易红外光谱检出、 低生物富集性和毒性特征的PBB分子修饰(以PBB-153为例). 研究结果表明, 构建的CoMFA模型对PBBs分子的红外振动强度、 生物富集性和毒性3种效应综合值具有较好的预测和拟合能力, 且具有较好的稳定性, 静电场和立体场的贡献率分别为59.9%和40.1%. 根据模型三维等势图选择正电性高于Br原子的5种取代基团对目标分子PBB-153进行单、 双取代, 筛选出6个3种效应综合值上升的PBB-153衍生物. PBBs衍生物分子单效应计算或预测结果验证表明所构建的兼具PBBs分子红外振动强度、 生物富集性和毒性3种效应综合值的CoMFA模型可以有效应用于PBBs分子的修饰. 设计的PBB-153衍生物分子具有较好的稳定性, 同时阻燃性与目标分子相当, 环境持久性及迁移性方面优于目标分子. 2D-QSAR模型表明, PBBs分子的偶极矩、 最负电荷及邻位Br原子数对其红外振动强度、 生物富集性和毒性单效应和综合值影响趋势一致.     

甘氨酸与氯化碱金属在水中的焓相互作用参数

氨基酸在混合溶液中的热力学性质及相互作用的研究不论对溶液化学还是生命科学都是十分重要的．对此国内已有不少的研究h，’1．利用偿效应的方法研究氨基酸与电解质间的相互作用是很有效的卜一句，但大多数的工作都是在低浓度下研究一个氨基酸分子和一个电解质离子对间的相互作用烩．本文测定了甘氨酸在水中和在LICI、NaCI、KCI的水溶液中的溶解偿，计算出甘氨酸与各个公在水中的偿对相互作用参数和三相互作用参数，并由此讨论了甘氨酸与这些盐的对分子相互作用和三分子相互作用．1实验部分试剂：甘氨酸为ARfa，K甲醇一水重结晶．LI…     

转动光谱学与微波光谱技术研究进展

转动光谱学是以量子力学为基础,研究分子、自由基,以及离子的转动光谱的基础科学,在天文观测以及大气成分监测等领域有着重要的应用。本文综述了转动光谱学的一些基本理论,两种傅里叶变换微波光谱仪的搭建原理,以及几种典型的微波光谱实例分析,并对微波光谱技术的未来发展做了展望。     

定量分析结构与纯液体介质光致克尔常数关系

对一系列液体分子进行了理论计算，运用多元回归分析建立了分子结构与纯液体介质光致克尔常数之间的定量关系，从光与分子作用和分子与分子间相互作用的角度对光致克尔效应进行了探讨。结果表明，纯液体介质的光致克尔常数与分子的前线轨道能级（能隙）、偶极矩和空间内最负的静电势之间存在着良好的线性相关关系。     

微波波谱法研究分子系统内基团大幅度运动动力学

分子中基团的运动方式、机制对分子体系性质、分子功能的表达等具有重要作用。微波波谱法在研究分子系统内部动力学、分子结构、构象变化、弱相互作用、基团大幅度运动以及探索量子溶剂等方面具有独特的能力,特别适合研究分子的精细结构、分子系统基团的内部转动运动,具有高灵敏度、高分辨率的特点。本文讨论了微波波谱法在研究分子系统基团大幅度运动动力学方面的应用,包括分子系统中甲基基团的内部转动、OH基团的运动、氨和氨基化合物的反演以及环状有机分子环运动等的动力学,同时结合作者使用微波波谱法研究的部分体系进行了分析。     

定量分子结构与纯液体介质光致克尔常数关系

对一系列液体分子进行了理论计算，运用多元回归分析建立了分子结构与纯液体介质光致克尔常数之间的定量关系，从光与分子作用和分子与分子间相互作用的角度对光致克尔效应进行了探讨。结果表明，纯液体介质的光致克尔常数与分子的前线轨道能级（能隙）、偶极矩和空间内最负的静电势之间存在着良好的线性相关关系。     

Dynamics of glass-forming liquids. VIII. Dielectric signature of probe rotation and bulk dynamics in branched alkanes

We have measured the dielectric relaxation of several glass forming branched alkanes with very low dielectric loss in the frequency range 50 Hz-20 kHz. The molecular liquids of this study are 3-methylpentane, 3-methylheptane, 4-methylheptane, 2,3-dimethylpentane, and 2,4,6-trimethylheptane. All liquids display asymmetric loss peaks typical of supercooled liquids and slow beta relaxations of similar amplitudes. As an unusual feature, deliberate doping with 2-ethyl-1-hexanol, 5-methyl-2-hexanol, 2-methyl-1-butanol, 1-propanol, or 2-methyltetrahydrofuran at the 1 wt % level generates additional relaxation peaks at frequencies below those of the alpha relaxation. The relaxation times of these sub-alpha-peaks increase systematically with the size of the dopant molecules. Because these features are spectrally separate from the bulk dynamics, the rotational behavior and effective dipole moments of the probes can be studied in detail. For the alcohol guest molecules, the large relative rotational time scales and small effective dipole moments are indicative of hydrogen bonded clusters instead of individual molecules.     

Entanglement of polar symmetric top molecules as candidate qubits

Proposals for quantum computing using rotational states of polar molecules as qubits have previously considered only diatomic molecules. For these the Stark effect is second-order, so a sizable external electric field is required to produce the requisite dipole moments in the laboratory frame. Here we consider use of polar symmetric top molecules. These offer advantages resulting from a first-order Stark effect, which renders the effective dipole moments nearly independent of the field strength. That permits use of much lower external field strengths for addressing sites. Moreover, for a particular choice of qubits, the electric dipole interactions become isomorphous with NMR systems for which many techniques enhancing logic gate operations have been developed. Also inviting is the wider chemical scope, since many symmetric top organic molecules provide options for auxiliary storage qubits in spin and hyperfine structure or in internal rotation states.     

Fourier transform microwave and millimeter wave spectroscopy of quinazoline, quinoxaline, and phthalazine

The pure rotational spectra of the bicyclic aromatic nitrogen heterocycle molecules, quinazoline, quinoxaline, and phthalazine, have been recorded and assigned in the region 13-87 GHz. An analysis, guided by ab initio molecular orbital predictions, of frequency-scanned Stark modulated, jet-cooled millimeter wave absorption spectra (48-87 GHz) yielded a preliminary set of rotational and centrifugal distortion constants. Subsequent spectral analysis at higher resolution was carried out with Fourier transform microwave (FT-MW) spectroscopy (13-18 GHz) of a supersonic rotationally cold molecular beam. The high spectral resolution of the FT-MW instrument provided an improved set of rotational and centrifugal distortion constants together with nitrogen quadrupole coupling constants for all three species. Density functional theory calculations at the B3LYP∕6-311+G?? level of theory closely predict rotational constants and are useful in predicting quadrupole coupling constants and dipole moments for such species.     

Microwave spectrum of cis-thiopropionic acid

The microwave spectrum of cis-thiopropionic acid in the ground vibrational state has been observed in the frequency range between 10 and 35 GHz. The rotational and centrifugal distortion constants, and the dipole moments have been determined. The conformation of this molecule is discussed on the basis of the observed results.     

Hydrogen bonded bimolecular complexes of carboxylic acids in the vapor phase : Observation and characterization by low resolution microwave spectroscopy

Various carboxylic acids and amides are shown to form H-bonded bimolecules with trifluoroacetic acid in the vapor phase. These bimolecules have been observed directly by low resolution microwave spectroscopy which gives rotational constants in agreement with those calculated with the assumption of a planar, 8-membered ring geometry for the H-bonded portion of the structure. A number of combinations did not provide observable spectra, and reasons are proposed why the bimolecules probably did not form in certain of these cases. Approximate dipole moments are obtained for the H-bonded bimolecular complexes.     

The study of dipole moment of some substituted acetic acids in an electronically excited state

The electronic absorption spectra of eight substituted acetic acids have been measured at room temperature in several solvents. The ground state dipole moments are evaluated experimentally for these molecules. These ground state values are used in conjunction with the spectral results to evaluate their first electronically excited state dipole moments. For all the molecules investigated here the dipole moments in the excited state are higher than their ground state values.     

Dielectric relaxation in OH—O bond complexes

Abstract

The dielectric absorption of the mixtures of Phenol with Acetone and Ethyl methyl ketone having different concentration ratios (3:1, 2:1, 1:1, 1:2 and 1:3) has been determined at microwave frequency 9.8 GHz, at 33°C. The dielectric data have been analyzed, to yield relaxation times and dipole moments, using Higasi method and Higasi, Koga and Nakamura method. All the mixtures yielded high values of the distribution parameter indicating the flexible nature of the OH-O type hydrogen bonding. The high values of the relaxation times and dipole moments give confirmative results for the association of the phenol with these electron donar molecules in all mixtures investigated.     

The sum rule for dipolar absorptions and rotational kinetic energy of wate and some dipolar molecules in condensed phases

Another form of the sum rule for dipolar absorptions has been derived by means of quantum statistics. The difference between this and usually used form results from a quantum effect on the molecular rotational motion. By the joint use of the two forms, average rotational kinetic energies of water molec in the liquid and solid phases and some dipolar molecules in solutions have been estimated. It has been shown that the average rotational kinetic energ larger than the value expected from the classical equipartition rule, with an increase in the hindering potential for the rotational motion of the mole The dipole moments of water molecules in liquid and solid water have been estimated. These are considerably smaller than the gas-phase value.     

Stark effect,polarizabilities and the electric dipole moment of heteronuclear diatomic molecules in 1Σ states

The theory of second-order Stark effect in ¹Σ states of heteronuclear diatomic molecules is thoroughly reviewed. The rigorous treatment given demonstrates that by introducing rotational, vibrational and electronic branch polarizabilities, the intrinsic character of the second-order Stark effect in diatomic molecules can be shown to be related more closely to polarizabilities than to dipole moments. The well-known expression for the Stark shift in ¹Σ levels which is dominated by the square of the dipole moment is only a crude, though sufficient approximation whenever large dipole moments are involved. For small dipole moments, however, this approximation is likely to fail, leading to an erroneous determination of such dipole moments. In the limiting case of negligible influence of the molecular rotation on the vibronic matrix elements, the arithmetic mean of the electronic branch polarizabilities turns out to be equal to the well-known static electronic polarizabilities α_∥ and α_⊥. The results are applied to the interpretation of the Stark splitting in the A¹Σ⁺, υ′ = 5, J′ = 1 level of ⁷LiH, recently determined by Stark quantum-beat spectroscopy.