采用分子动力学方法研究氯化钠水溶液的微观结构

溶液的微观结构对溶液的宏观性质具有决定性影响,团簇的存在和溶液不均性的认知是该领域研究的重要进展之一,也是关注的热点.为了考察溶液的微观结构,本文采用分子动力学方法对浓度适中的氯化钠水溶液进行了模拟,获得了各原子(离子)间的径向分布函数和溶液的瞬态图像.通过对比分析Na~+-Cl~-和Cl~--Na~+的径向分布函数,并结合已有研究结果,表明该径向分布函数上第三峰也来源于离子对,发现氯化钠水溶液存在着第三种离子对;上述径向分布函数上的三个峰分别与直接接触离子对、部分间隔离子对和完全间隔离子对相对应,并给出了这三种离子对的瞬态图像.三个时刻下系统瞬态图像的分析结果表明,溶液中存在水分子连续分布的区域和由离子与水分子共同构成的离子团簇.各瞬态图像中水分子连续分布的最大区域的平均尺寸至少为1.43 nm,溶液中部分间隔离子对的比例最大,约为0.68.在同时考虑直接接触离子对和部分间隔离子对时,三个时刻中最大团簇尺度的平均值为1.44 nm,该值约为部分间隔离子对最概然尺寸的3倍;团簇尺寸随团簇中离子数的增加而增大,在团簇中离子数较大时,满足无规行走(自由连接链)模型的结果.这些说明氯化钠水溶...     

高盐溶液蒸发过程中的分子动力学模拟与研究

随着我国工业的快速发展,如何减量化处理工业排放的高盐废水已经成为了亟待解决的环境问题.在处理高盐废水的各种工艺中,热蒸发技术因具备脱盐效果好,灵活性好等特点得到了广泛应用.本文从微观角度出发,采用分子动力学模拟方法研究了LiCl、KCl、CaCl₂三种溶液在400 K和500 K两种温度加热条件下的蒸发过程,分析了Li⁺、K⁺、Ca²⁺,Cl^-四种盐离子对蒸发速率、水分子取向、氢键、溶液结构等性质的影响.研究结果表明温度的提升会对蒸发速率产生极大影响,温度的提高不会改变配位水化层的位置但会明显减少离子的配位水分子数,有利于提高活跃水分子的占比和蒸发速率.     

应用分子动力学模拟和拉曼光谱对钙、镁、氯离子 水化现象的研究

应用分子动力学方法,模拟了298 K下,密度为1.0 g/cm~3的水溶液中Ca²⁺,Mg²⁺,Cl~-的水化现象,得到了相应离子周围水分子的微观分布情况.发现在钙离子周围,水分子以其氧离子去靠近中心离子;而在氯离子周围,水分子则以其中的一个氢原子去靠近中心离子.通过分析三种离子的径向分布函数、配位数曲线、水化数、水化半径,发现Ca²⁺的水化数和水化半径均大于Mg²⁺,即Ca²⁺的水合能力比Mg²⁺强.与以往研究结果相比,本文计算所得的自扩散系数更接近实验所得结果.为了使模型更好的代表真实水溶液体系,本文还应用分子动力学和拉曼光谱法研究了不同浓度的CaCl₂水溶液.分子动力学研究发现随着浓度的升高,CaCl₂溶液中Ca²⁺,Cl~-的配位数分别呈降低趋势.同时,随着浓度的升高,Ca²⁺,Cl~-的自扩散系数也呈现降低的趋势.作者推断这是由于浓度的升高,加剧了离子的微观反...     

乙醚团簇在纳秒激光场中的多价电离及其电子能量分布的研究

用5ns,1064nm的脉冲Nd:YAG激光,研究了乙醚团簇与纳秒激光的相互作用.在10¹¹ W/cm²量级光强下,观察到价电子完全剥离的O⁶⁺,C⁴⁺,且这些高价离子的强度比值基本不随激光能量而变化.用阻滞电压方法测量了电离过程中溢出电子能量分布,在最大激光能量4.0×10¹¹ W/cm²,溢出电子的平均能量为56eV,最大能量为102eV.实验结果支持了高价离子产生的“多 关键词： 高价离子 电子能量 纳秒激光 乙醚团簇     

自受激拉曼晶体Nd3+:SrMoO4的光谱性质研究

通过拉曼散射光谱，吸收光谱，荧光发射寿命和808 nm LD激发下的红外荧光光谱的实验测量，系统研究了Nd³⁺:SrMoO₄晶体的自受激拉曼光谱性质.分析指认了拉曼散射光谱中各拉曼峰所对应的晶格振动模式，得出了其SRS活性最强的声子频率约为898 cm^-1，对应于(MoO^2-₄)离子团的完全对称光学伸缩振动A_g模；通过J-O理论对晶体的吸收谱进行了全面的光谱参数计算，得出⁴F_3/2→⁴I_11/2跃迁的积分发射截面达0.57×10^-18 cm²，自发辐射概率为141.06 s^-1；同时，实验测得该跃迁的荧光发射寿命约为0.2 ms.最后，结合808 nm LD激发下的红外波段荧光光谱，论证了SrMoO₄晶体中Nd³⁺离子1068 nm发射通过拉曼频移获得1180 nm一级斯托克斯激光发射的可能性，为Nd³⁺:SrMoO₄晶体的自受激拉曼激光器研究提供了理论依据. 关键词： 3+离子')" href="#">d³⁺离子 4 晶体')" href="#">SrMoO₄ 晶体 自受激拉曼散射     

H+2，H+3团簇离子在沟道条件下的背散射 质子产额测量

采用卢瑟福背散射方法，测得了每质子能量为650 keV的H⁺₂，H+₃团簇离子在Si晶体<100>和<110>沟道条件下的质子背散射能谱.结果发现，由于H⁺₂，H⁺₃团簇在晶体中的库仑爆炸和团簇效应，H⁺₂的背散射质子产额大于H ⁺的背散射产额，而H^{+< 关键词： 团簇 沟道效应 库仑爆炸 背散射}     

355 nm激光光电离甲醛飞行时间质谱的研究

利用脉宽为5 ns脉冲Nd: YAG 355 nm激光在功率密度为10¹¹–10¹² W/cm²条件下实现了甲醛含水团簇多光子电离, 并用飞行时间质谱对其电离产物和电离过程进行了研究. 实验中观测到了甲醛的质子化团簇系列 (CH₂O)_nH⁺(n=1–4), 甲醛的去质子化团簇系列(CH₂O)_nCHO⁺ (n=1–3), 以及两个起源于H₂CO去质子和质子化的含水团簇系列HCO⁺(H₂O)_n(n=1,3,5)和H₃CO⁺(H₂O)_n(n=1,3,5), 并对其中的一些团簇结构构型进行了猜测. 研究在不同的激光功率密度下甲醛团簇质谱峰的变换情况, 当激光密度达到9.3× 10¹¹ W/cm², 开始出现CH₂O和H₂O本体及其光致碎片的信号, 但对应的各质量峰没有明显地分辨开, 而是以包络的形式出现, 这是激光电离产生高能离子释放的一种表现, 提出认等离子体动力学鞘层加速机制(模型)来解释高能离子形成的物理机制. 关键词： 甲醛 团簇 飞行时间质谱 激光电离     

基于FRET机理的荧光探针的合成及其对汞离子的识别

基于FRET机理设计合成了一个包含罗丹明6G及香豆素的汞离子荧光探针Rh-6G-coumarin(RC),研究了它的光谱性能及对汞离子的识别作用。在V(C₂H₅OH)∶V(H₂O)=9∶1溶液中加入汞离子后,575 nm处荧光强度迅速增大,荧光由蓝色变为明亮的红色,同时溶液的颜色由黄色变为红色。溶液中其他金属离子,如Na⁺、K⁺、Mg²⁺、Fe²⁺、Co²⁺、Pb²⁺、Zn²⁺、Cd²⁺和Cr³⁺对汞离子的荧光识别没有太大影响。该探针可在较宽的pH ( 4~10)范围内识别汞离子。光谱滴定实验表明,汞离子与RC以2∶1的计量比形成了配合物。     

K离子掺杂增强NaErF4体系上转换发光

制备了一系列Na_1-xK_xErF₄@NaLuF₄的核壳纳米结构,核中K⁺掺杂摩尔分数变化范围为0%~8%。XRD分析结果揭示这些具有不同K掺杂浓度的纳米粒子均为β-相纳米结构。研究结果表明：随着K⁺浓度的增加,纳米结构中Er³⁺~650 nm处的红带发光强度呈现先增强后减弱的规律,当K⁺摩尔分数为4%时,Na_0.96K_0.04ErF₄@NaLuF₄纳米晶的发光强度达到最大,为未掺杂K⁺的NaErF₄@NaLuF₄纳米晶发光强度的3.7倍。其发光增强的原因在于K⁺的掺杂降低了Er³⁺微环境晶场宇称对称性,提高了Er³⁺离子⁴F_9/2→⁴I_5/2能级辐射跃迁几率,进而增强了Er³⁺的650 nm红带的上转换发光强度。     

调幅W(Mo)/Cu纳米多层膜He+离子辐照响应行为

用磁控溅射技术制备不同调幅波长 (L) 的W(Mo)/Cu纳米多层膜,所制膜系在60 keV氦离子 (He⁺) 辐照条件下注入不同剂量: 0, 1×10¹⁷ He⁺/cm², 5×10¹⁷ He⁺/cm². 用X射线衍射仪 (XRD) 和高分辨透射电子显微镜(TEM)表征W(Mo)/Cu纳米多层膜辐照前后微观结构. 研究结果表明: 1) He⁺离子轰击引起温升效应是导致沉积态亚稳相β-W 转变成稳态 α-W相的主因, 而与调幅波长无明确关联; 2) 纳米多层结构中W(Mo) 和Cu膜显现出的辐照耐受性与调幅波长相关, 调幅波长越小, 抗He⁺的辐照性能越强; 3) 在5×10¹⁷ He⁺/cm²注入条件下, 观察到He团簇/泡在纳米结构W(Mo) 和Cu膜中的积聚行为存在明显差异: 在W (Mo) 膜中He团簇/泡的分布与晶粒取向相关, He团簇/泡倾向于沿W (211) 晶面分布; 而Cu膜非晶化且He团簇/泡在其体内呈均匀分布. 关键词： W(Mo)/Cu纳米多层膜 +辐照')" href="#">He⁺辐照 He团簇/泡 相转变     

The effect of ion pairs on water structure

A Monte Carlo study of lithium chloride and potassium fluoride in water clusters is reported. The ion-water and water-water interactions are modelled using Hartree-Fock potentials. Results are given for clusters of 50 molecules with a fixed ion-ion distance of 4 Å at a temperature of 298 K. It is shown that all four ions have strongly bound first-neighbour shells and that some water structure is discernible beyond the second-neighbour shell. When ion pairs are close together, as in this study, their coordination numbers are not independent.     

Microscopic structure of liquid dimethyl sulphoxide and its electrolyte solutions: molecular dynamics simulations

Molecular dynamics (MD) simulations of pure dimethyl sulphoxide (DMSO) and solutions of Na⁺, Ca²⁺, Cl^?, NaCl and CaCl₂ in DMSO have been performed at 298.15 K and 398.15 K in NVT ensembles by using a four-interaction-site model of DMSO and reaction field method for Coulombic interactions. The structure of solvent, ion-solvation shells and ion-pairs have been analysed by employing a concept of coordination centres and characteristic vectors of the solvent molecule. Results are given for atom-atom (corresponding to DMSO), ion-atom and ion-ion radial distribution functions (RDFs), orientation of the DMSO molecules and their geometrical arrangements in the first solvation shells of the ions (Na⁺, Ca²⁺, Cl^?). A preferential formation of cyclic dimers with antiparallel alignment between dipole moments of nearest-neighbour molecules in the pure solvent is found. Geometrical models of the first coordination shells of the ions in ‘infinitely dilute solutions’ are proposed. Ion-ion RDFs in NaCl-DMSO and CaCl₂-DMSO solutions reveal the presence of both solvent separated (SSIP) and contact (CIP) ion pairs. The structures of the solvation shells of such ion pairs are also discussed.     

Crystal fields of hexameric rare-earth clusters in fluorites

In solid solutions of alkaline-and rare-earth fluorides with a fluorite structure, ions of most elements of the rare-earth (RE) row form hexameric clusters that assimilate the minor component of the solid solutions (fluorine) and build it into the cubic fluorite lattice without changing its shape. An analysis of the EPR spectra of paramagnetic RE ions (Er³⁺, Tm³⁺, Yb³⁺) in clusters of diamagnetic ions (Lu³⁺, Y³⁺) confirms their hexagonal structure, which was established when studying the superstructures of the compounds under study. In such a cluster, a RE ion is in a nearly tetragonal crystal field, with the parameters of this field differing radically from those of single cubic and tetragonal RE centers in crystals with a fluorite structure. In particular, this field causes high (close to limiting) values of the g_∥ factors of the ground states of the paramagnetic RE ions. Computer simulation is used to determine the atomic structure of a hexameric cluster in MF₂ crystals (M = Ca, Sr, Ba). The crystal field and energy spectrum of Er³⁺, Tm³⁺, and Yb³⁺ ions in such clusters are calculated, and the spectroscopic parameters of the ground states of these ions are determined. The calculations confirm the earlier assumption that the unusual EPR spectra of nonstoichiometric fluorite phases are related to RE ions in hexameric clusters.     

Electrical conductivity and colour centres in Tl-doped KCl crystal

The electrical conductivity and optical absorption of potassium chloride crystals doped with different concentrations of thallium have been measured before and after X-irradiation. The optical absorption spectrum exhibits the characteristic Tl⁺ ion band at 247 nm. The extrinsic conductivity and the absorption coefficient at 247 nm increase with impurity addition upto a certain concentration. Further increase in impurities decreases them. Room temperature X-irradiation decreases the Tl⁺ ion band and produces the F band. F centre concentration is higher in lightly doped crystal compared to pure or heavily doped KCl. These results have been interpreted in terms of formation of interstitial potassium ions and positive ion vacancies in the Tl-doped KCl lattice due to large ionic radius of Tl⁺ ions. The impurity ions precipitate into TlCl phase when the doping is heavy.     

First stage f centre formation in pure and doped KCl crystals by room temperaure X-irradiation

The electrical conductivity and optical absorption of potassium chloride crystals, pure and doped with divalent cation impurities, have been measured before and after X-irradiation at room temperature. The concentration of free positive ion vacancies at room temperature has been calculated from conductivity for each crystal before irradiation and is found to be much less than the first stage F centre concentration. This shows that both free and associated positive ion vacancies are the latent source of F centres in the first stage colouration. Pb^{+ +} ions trap electrons producing Pb^{+ +} and Pb⁰ centres and making free the associated cation vacancies. Such centres are not produced in Ca-doped crystals where impurity-vacancy complexes trap F centres producing Z centres. The higher ratio of F centres to positive ion vacancies in Pb-doped crystals indicates that free cation vacancies are more effective in producing F centres. However, the concentration of divalent cations is found to decrease in both the crystals after irradiation, the decrease being more in Ca-doped crystals.The author is indebted to Prof. H. N. Bose for helpful discussions. Thanks are also due to Dr. M. L. Mukherjee for providing the crystals.     

A study of KCL lattice defects by thermoluminescence experiments

The thermoluminescent emission of X-irradiated potassium chloride is recorded simultaneouslyvs. temperature and wavelength. Samples of different origin and prepared through different processes, including thermal treatments, are examined. Most records show essentially two glow peaks, the wavelength of the one at higher temperature being slightly shifted toward the red. On the whole, experimental results suggest that luminescent centres are originated by potassium ion vacancies lying at a variable distance from interstitial potassium ions. The observed red shift is ascribed to the Coulomb energy of the pairs of these point defects of opposite charges.     

On the question of Bi(III) complexes in NaCl

The absorption of trivalent bismuth in solutions of sodium chloride of different concentrations was studied. The absorption bands were ascribed to complexes of bismuth with chlorine. The agreement between absorption bands in NaCl and KCl crystals doped with bismuth and in sufficiently concentrated solutions shows that bismuth in these crystals forms an octahedral complex with six neighbouring chlorine ions.     

A method for estimating the local lattice distortions near a magnetic ion from ligand hyperfine parameters: Yb3+trigonal centers in SrF2 and BaF2

An empirical relationship describing the radial dependence of the nondipole part of the anisotropic constant for the ligand hyperfine interaction in alkaline-earth fluorides is proposed. This relationship is used for calculating the distances between the magnetic ion and the fluorine ions involved in its nearest environment. The results of the calculations are in good agreement with the values obtained by other methods for both cubic and tetragonal fluorine centers in these crystals. The distances from the magnetic ion to different groups of nonequivalent fluorine ions of the nearest environment in Yb³⁺ trigonal centers of SrF₂ and BaF₂ are determined. It is found that the Yb³⁺ ion is slightly displaced along the trigonal axis away from the compensating fluorine ion.     

Effect of the valence state of ce ions on the phase stability and mechanical properties of the crystals of ZrO<Subscript>2</Subscript>-based solid solutions

The structure and mechanical properties of the crystals of solid solutions of zirconium dioxide, which are stabilized by yttrium and cerium oxides, have been studied. The electron paramagnetic resonance technique has been used to identify Ce³⁺ ions and to determine their relative concentration in the crystals. It is shown that the presence of Ce³⁺ ions in the crystals is the main factor responsible for their high fracture toughness. The annealings carried out during investigations, which lead to a decrease in the concentration of Ce³⁺ ions, show that a change in the valence state of cerium ions lowers the fracture toughness of the crystals.