氯化钙甲醇溶液中离子溶剂化作用的理论研究

利用红外光谱研究不同温度下CaCl2/甲醇溶液体系的溶剂化作用,结果表明在溶液中CaCl2以离子形式与甲醇发生溶剂化作用,且溶剂化数随温度升高而降低.通过密度泛函理论（DFT）在B3LYP/6-31G＊＊水平下对CaCl2/甲醇溶液中可能存在的配位构型进行结构优化及热力学性质的计算,说明了在CaCl2/甲醇溶液中各种配位构型存在的可能性,得出温度升高热力学数据的变化规律,解释了溶剂化数随温度升高而降低的趋势.进一步对各种可能配位构型的红外吸收频率进行计算并与实验结果进行比较,推断在CaCl2/甲醇溶液中主要存在的配位构型为[CaCl（CH3OH）n]＋和[Cl（CH3OH）n]-.     

甲醇团簇的多光子电离质谱及其从头算

用355 nm激光对脉冲分子束超声膨胀冷却的甲醇分子进行多光子电离, 飞行时间质谱仪观测到除甲醇碎片离子外的质子化甲醇团簇(CH3OH)nH+(n=1-16), 且离子的种类及相对强度与激光相对于脉冲分子束的延时无关, 取决于团簇离子内在结构的稳定性. 结合从头算密度泛函理论, 在B3LYP/6-31G(d)基组水平上优化得到了(CH3OH)n和(CH3OH)nH+(n=1-4)的稳定构型. 振动频谱分析显示, 团簇中最强的红外振动模主要来自氢键H伸缩振动的贡献. 团簇电离后发生于团簇内的质子转移反应也可能与激光电离引起的与氢键有关的振动模激发密切相关.     

温度对LiCl和LiNO3/N,N-二甲基甲酰胺溶液结构的影响

研究了N,N-二甲基甲酰胺(DMF)纯溶剂、不同浓度LiCl/DMF和LiNO3/DMF溶液的红外光谱,得到随着温度升高,发生溶剂化作用的DMF分子比例不断降低,阴阳离子对构型比例逐渐增加的规律.采用密度泛函理论计算验证了红外谱图随温度升高变化的实质,得出溶液中存在的团簇构型主要为阴阳离子对构型(LiCl(DMF)n和LiNO3(DMF)n),阳离子构型[Li(DMF)n]+和阴离子构型([Cl(DMF)n]-,[NO3(DMF)n]-)的结论.     

线型碳链PC2nP的结构和电子光谱的密度泛函理论研究

应用密度泛函理论,在B3LYP/6-31G**和B3LYP/6-311G**水平上优化得到了线型簇合物PC2nP(n=1-10)的基态平衡几何构型,计算了它们的谐振动频率.在基态平衡构型下,利用含时密度泛函理论,计算得到了簇合物PC2nP(n=1-10)的垂直激发能和相应的振子强度,导出了激发能与体系大小n的解析关系式.     

纳米银粒子对[Ru(bpy)_3]~(2+)光谱学性质的影响及电解质效应

研究了[Ru(bpy)3]2+溶液中引入纳米银粒子的光谱学性质变化规律以及[Ru(bpy)3]2+与纳米银粒子所构成的溶液体系([Ru(bpy)3]2+-Ag)的电解质效应.研究结果表明,[Ru(bpy)3]2+吸附在纳米银粒子表面使纳米银粒子相互桥连形成规则的类链状网络聚集体.纳米银粒子造成[Ru(bpy)3]2+溶液荧光猝灭,且大尺寸的纳米银粒子引起的荧光猝灭程度较大.在[Ru(bpy)3]2+-Ag体系中引入电解质造成纳米银粒子不同程度的聚集和生长.电解质对纳米银聚集影响为:CaCl2MgCl2Ca(NO3)2KClKNO3.随着[Ru(bpy)3]2+-Ag体系中引入电解质含量的增加,溶液的荧光强度先降低而后又逐渐增强,直至达到定值,表明一定量的电解质可产生荧光猝灭释放效应.电解质对荧光强度影响顺序为:Ca(NO3)2CaCl2MgCl2KClKNO3.采用透射电子显微镜、紫外-可见吸收分光光度计和荧光分光光度计等手段从分子间相互作用和能量传输等方面初步探讨了纳米银粒子对表面吸附[Ru(bpy)3]2+溶液光谱学性质的影响机制以及电解质效应.     

氨和甲醇团簇中的质子转移反应

应用激光多光子电离质谱和分子束技术研究了氨和甲醇二元团簇,实验观测到两个系列质子化的团簇离子: (CH3OH)nH+和(CH3OH)nNH4+(1≤n≤14 ),其产生是经过二元团簇内的质子转移反应。同时也研究了氘代甲醇CH3OD和氨混合团簇,结果表明OD原子团中的D转移概率比CH3原子团中的质子转移概率大几倍。在HF/STO-3G和MP2/6-31G*　*水平上对氨和甲醇二元团簇进行了计算,结果表明与CH3相比OH中的质子转移更加容易,因为CH3中的质子转移过程要克服高度约120 kJ/mol的能垒。     

硅氧团簇(SiO2)nO2H4的密度泛函理论研究

提出硅氧团簇(SiO2)nO2H4的两种新构型: 基于笼状结构和环状结构的构型, 并与链状构型相比较, 用密度泛函理论的B3LYP方法在6-31G(d)基组水平上计算了三种构型n=2～22(n取偶数)的几何结构、平均结合能、能隙以及能量的二次差分. 分析计算结果发现, 笼状构型不但在n=4和8处存在幻数团簇(实验上已经观察到), 而且预测在n=14处也存在类似的幻数团簇; 此外, 与(SiO2)n团簇不同的是, (SiO2)nO2H4团簇的环状构型的稳定性从n=4开始大于链状构型, 意味着水的加成对硅氧团簇的稳定性有着重要的影响.     

(Mg3N2)n(n=1～4)团簇结构与性质的密度泛函研究

用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G*基组水平上对(Mg3N2)n(n=1～4)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的振动特性、成键特性、电荷特性和稳定性等进行了理论分析.结果表明:(Mg3N2)n=1～4团簇易形成笼状结构,其最稳定构型中N原子配位数以3、4较多见;团簇主要由Mg-N键组成,Mg-N键长为0.194～0.218nm,Mg-Mg 键长为0.262～0.298 nm;N原子的平均自然电荷为-2.06 e,Mg原子的平均自然电荷为 1.37 e;(Mg3N2)2团簇有相对较高的动力学稳定性.     

[Ca(NH2)2]n (n＝1～5)团簇的密度泛函理论研究

用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G*基组水平上对[Ca(NH2)2]n (n＝1～5)团簇各种可能的构型进行几何结构优化, 预测了各团簇的最稳定结构. 并对最稳定结构的振动特性、成键特性、电荷特性等进行了理论研究. 结果表明: 团簇易形成环状结构, 以金属Ca原子团簇作为骨架, NH2基结合在金属团簇骨架上, 并主要是Ca—N成键和Ca—Ca成键. 团簇中Ca—N键长为0.225～0.257 nm, Ca—Ca键长为0.312～0.354 nm, N—H键长为0.102～0.103 nm, H—N—H键角为102.9°～104.2°; 团簇中Ca原子的自然电荷在1.657e～1.720e之间, N原子的自然电荷在－1.543e～－1.592e之间, H原子的自然电荷在0.349e～0.367e之间, Ca原子和NH2基之间相互作用呈现较强的离子性;对比团簇和晶体的结构及IR谱表明, NH2基在团簇和晶体中的结构基本一致.     

簇合物(F2GaN3)n(n=1～4)的理论研究

采用密度泛函理论B3LYP/6-311+G*方法,计算研究了(F2GaN3)n(n=1～4)簇合物的结构和性质.研究表明,簇合物(F2GaN3)n(n=2～4)的优化构型均拥有Ga-Na-Ga连接的环状结构.讨论了几何参数随聚合度的变化关系.三聚体的船式构象较椅式构象的能量低16 kJ·mol-1,具有S4对称性的四聚...     

第一性原理对Sr2 /甲醇溶液微团簇结构的分析

利用光谱实验和第一性原理研究了SrCl2/甲醇溶液中离子的溶剂化微团簇现象。计算采用B3LYP中6-31G(d,p)基组和TPSSTPSS中LANL2DZ基组。通过对低浓度锶甲醇溶液中可能存在的团簇构型进行优化和热力学常数计算,获得了溶液中较稳定的微团簇构型及其构型随浓度变化相互转化的规律。     

DFT Calculation of Glycine with Methanols Clusters

Density functional theory （DFT） calculations are reported for the structures of neutral and zwitterionic glycine-（CHaOH）n where n=1-6. Initial geometries of the clusters of neutral and zwitterionic glycine with 1-6 methanol molecules are fully optimized at B3LYP/6-31＋G^＊ level of theory. The lowest energy configurations are located and their hydrogen bond structures are analyzed. Theoretical prediction reveals that the methanols prefer to locate near the carboxylic acid group for the small clusters （n_〈3） with the neutral form while the configurations with the methanols bridging the acid and the amino group are favorite in the zwitterionic form clusters. When the number of the methanol molecules in the clusters reaches five and six, the two forms tend to be isoenergetic.     

Fluorescence quenching in cyclic hydrogen-bonded complexes of 1H-pyrrolo[3,2-h]quinoline with methanol: cluster size effect

Laser induced fluorescence (LIF) excitation spectra of molecular complexes of 1H-pyrrolo[3,2-h]quinoline (PQ) with methanol (n= 1, 2, 3) as well as vibrational spectra of their electronic ground state are reported. The latter have been recorded in the mid-infrared region by fluorescence depletion (FDIR). The only PQ.methanol(n) complex clearly identified in the LIF spectrum is the triply hydrogen-bonded cyclic 1 ratio 2 aggregate. Its stoichiometry has been proven by the femtosecond multiphoton ionization detected infrared measurements [J. Am. Chem. Soc., 2006, 128, 10 000]. The structure of the 1 ratio 2 cluster is determined by means of FDIR spectroscopy in combination with ab initio and DFT calculations. No fluorescence was detected that could be attributed to the 1 ratio 1 cluster. This behaviour of the 1 ratio 1 complex is explained in terms of rapid excited state double proton transfer followed by a non-radiative relaxation. The n= 3 and heavier clusters are fluorescent. Their electronic spectra overlap, preventing the selective measurement of the FDIR spectra of individual complexes.     

5-巯基-1, 3, 4-噻二唑-2-硫酮微溶剂团簇的光谱和理论计算研究

微溶剂作用(即溶剂化过程)广泛存在于所有物理、 化学和生命过程中. 在液相化学反应体系中, 几乎是一切化学反应的基础. 通过傅里叶变换拉曼光谱(FT-Raman)并结合密度泛函理论(DFT), 表征了固态5-巯基- 1, 3, 4-噻二唑-2-硫酮(MTT)的结构, 并进一步确认了MTT在乙腈、 甲醇和水中微溶剂团簇的大小和氢键位点. 通过探究MTT在不同溶剂及pH条件下的紫外-可见吸收光谱(UV-Vis), 结合含时密度泛函理论(TD-DFT)计算, 揭示了溶剂和pH对MTT电子跃迁带的影响, 进一步解释了其光谱位移. 结合能量计算可以得出, MTT分别与1个乙腈、 2个甲醇和2个水分子形成MTT(CH₃CN), MTT(CH₃OH)₂ 和MTT(H₂O)₂团簇.     

Theoretical analyses of the morphological development of the hydrogen bond network in protonated methanol clusters

Extensive density functional theory (DFT) calculations are carried out on various structural isomers of protonated methanol clusters, H(+)(MeOH)n (n = 2-9), to analyze the morphological development of the hydrogen bond network in the clusters with an increase of the cluster size. Coexistence of multiple structural isomers is demonstrated by the nearly degenerated energies. Moreover, significant temperature dependence of the preferential isomer structure is shown by the calculated Gibbs free energies. The previously reported infrared spectra of H(+)(MeOH)n (J. Phys. Chem. A 2005, 109, 138) are revisited on the basis of the spectral simulations of the isomers by DFT calculations.     

How Many Methanol Molecules Can Solvate a Glycine: a PBE1PBE Approach

Microsolvation of glycine in methanol clusters is explored by the use of DFT calculation method. The lowest energy conformations within 16.72 kJ·mol-1 of the glycine clustering with one to six methanol molecules, which are obtained at the B3LYP/6-31+G(d) level of theory, are reoptimized at PBE1PBE/6-311+G(d,p). The calculated results agree with our previous results with B3LYP (Chin. J. Chem. Phys. 22 (2009) 577) that the clusters of two forms (Z-and N-form) tend to be isoenergetic when the number of the solvate molecules reaches six. Furthermore, this result is in good agreement with the experiment of the tryptophan-methanol clusters, implying that the present treatments are reasonable and reliable. The results also indicate that nine methanol molecules are not enough to fully solvate a glycine molecule, and a tentative estimation is obtained that ten methanol molecules may fully solvate a glycine molecule, which consists with the experiment results.     

Hydrogen bonding in methanol clusters probed by inner-shell photoabsorption spectroscopy in the carbon and oxygen K-edge regions

Hydrogen bonding in methanol clusters has been investigated by using inner-shell photoabsorption spectroscopy and density functional theory (DFT) calculations in the carbon and oxygen K-edge regions. The partial-ion-yield (PIY) curves of H(CH(3)OH)(n)(+) were measured as the soft x-ray absorption spectra of methanol clusters. The first resonance peak in the PIY curves, which is assigned to the sigma*(O-H) resonance transition, exhibits a 1.20 eV blueshift relative to the total-ion-yield (TIY) curves of molecular methanol in the oxygen K-edge region, while it exhibits a shift of only 0.25 eV in the carbon K-edge region. Decreased intensities of the transitions to higher Rydberg orbitals were observed in the PIY curves of the clusters. The drastic change in the sigma*(O-H) resonance transition is interpreted by the change in the character of the sigma*(O-H) molecular orbital at the H-donating OH site due to the hydrogen-bonding interaction.     

Adsorption energies of molecular oxygen on Au clusters

The adsorption properties of O(2) molecules on anionic, cationic, and neutral Au(n) clusters (n=1-6) are studied using the density functional theory (DFT) with the generalized gradient approximation (GGA), and with the hybrid functional. The results show that the GGA calculations with the PW91 functional systemically overestimate the adsorption energy by 0.2-0.4 eV than the DFT ones with the hybrid functional, resulting in the failure of GGA with the PW91 functional for predicting the adsorption behavior of molecular oxygen on Au clusters. Our DFT calculations with the hybrid functional give the same adsorption behavior of molecular oxygen on Au cluster anions and cations as the experimental measurements. For the neutral Au clusters, the hybrid DFT predicts that only Au(3) and Au(5) clusters can adsorb one O(2) molecule.     

DFT和热力学研究氢键协同效应及对关联1H NMR的影响

用DFT方法在B3LYP/6-311＋＋G (d,p)水平下研究了甲醇线性和环状分子簇. 对于不同大小的分子簇之间定义了协同因子. 计算得到的协同因子可以验证氢键的强协同效应, 环状分子簇之间的协同效应远远大于线性分子簇. 做为理论验证和比较, 热力学模型分别采用含氢键缔合的格子流体状态方程(LFHB), 以及含氢键协同效应的LFHB, 关联醇-惰性体系的¹H核磁共振化学位移. 考虑协同效应的关联结果优于原始的LFHB. 比较量子化学计算的和热力学模型中采用的协同因子, 认为甲醇和乙醇在溶液中更可能大部分以线性缔合形式存在.     

DFT和热力学研究氢键协同效应及对关联1H NMR的影响

用DFT方法在B3LYP／6—311 G(d,p)水平下研究了甲醇线性和环状分子簇．对于不同大小的分子簇之间定义了协同因子,计算得到的协同因子可以验证氢键的强协同效应,环状分子簇之间的协同效应远远大于线性分子簇,做为理论验证和比较,热力学模型分别采用含氢键缔合的格子流体状态方程(LFHB),以及含氢键协同效应的LFHB,关联醇一惰性体系的^1H核磁共振化学位移．考虑协同效应的关联结果优于原始的LFHB,比较量子化学计算的和热力学模型中采用的协同因子,认为甲醇和乙醇在溶液中更可能大部分以线性缔合形式存在。