烷烃客体分子(C_nH_m,n≤6,m≤14)在5~(12)6~2和5~(12)6~4水笼中的稳定性与拉曼光谱的密度泛函理论计算

可燃冰矿藏中气体成分非常复杂,通过谱学分析对水合物样品成分进行指认具有重要意义.基于B97-D/6-311++G(2d,2p)的密度泛函理论(DFT)计算,我们系统地探索了构成水合物的两种标准水笼(51262和51264)包络十八种不同烷烃客体分子的稳定性.从计算结果可以看出,除了3-甲基戊烷和2,3-二甲基丁烷两个烷烃客体分子,其它16个烷烃客体分子都可以被容纳在51262笼中;但是与51262笼不同,十八种烷烃客体分子都可以被容纳在尺寸较大的51264笼中.同时,我们也模拟了五种直链烷烃和四种环状烷烃在51262和51264笼中相应的谱学特征,从拉曼谱图上可以看出,随着碳原子数量的增多,直链烷烃客体分子C―H键伸缩振动区的多数拉曼谱带向高波数移动,而环状烷烃客体分子C―H键伸缩振动区的拉曼谱带则向低波数移动.这些结果为实验上通过拉曼谱测量指认水合物矿藏的成分提供理论参考.     

N2O+经由B2Пi←X2П跃迁的光解离机理研究

在超声分子束条件下,利用360.50 nm的电离激光使N₂O分子经由[3+1]共振增强多光子电离（REMPI）产生纯净的N₂O⁺（X²Π（000））分子离子,用另一束解离激光在230-275 nm范围扫描获得N₂O⁺经由B²П_i←X²Π跃迁产生的光解碎片（NO⁺和N₂⁺）激发（PHOFEX）谱. 获得的光解碎片激发谱可以归属为B²П_i（00n）←X²Π（000）序列跃迁. 我们分别将线性三原子分子离子N₂O⁺中N―N伸缩振动简化成NO和N之间的简谐振动,N―O伸缩振动简化成N₂和O之间的简谐振动,用谐振子的简谐势能曲线和波函数对N₂O⁺分子离子X²Π和B²П_i电子态振动能级间跃迁的Franck-Condon因子进行计算,和实验得到的碎片离子增强谱实验强度进行比较,对前人给出的分子数据（分子平衡核间距）进行验证,讨论了N₂O⁺经由B²П_i（00n）←X²Π（000）电子态跃迁的光解离机理和碎片离子的分支比.     

Li＋在基于N,N-二甲基甲酰胺混合溶剂中的溶剂化

利用红外和拉曼光谱技术研究了Li^＋在不同浓度、不同溶剂组成的LiBF₄/N,N-二甲基甲酰胺-乙腈、LiBF₄/N,N-二甲基甲酰胺-四氢呋喃电解质溶液中的优先溶剂化现象. 红外和拉曼光谱的分析表明, Li^＋主要与DMF分子相互作用, 导致该分子的C＝O伸缩振动谱带、N—C＝O形变谱带、CH₃摇摆谱带等发生了分裂. Li^＋与其它溶剂分子的相互作用较弱, 谱带的分裂现象并不明显. Li^＋溶剂化数的计算显示, Li^＋第一溶剂化层内DMF分子的数目一般大于2, 这说明 Li^＋在混合溶剂体系内优先与DMF分子相互作用. 量子化学计算支持了这一结论.     

Li＋在基于N,N-二甲基甲酰胺混合溶剂中的溶剂化

利用红外和拉曼光谱技术研究了Li^＋在不同浓度、不同溶剂组成的LiBF₄/N,N-二甲基甲酰胺-乙腈、LiBF₄/N,N-二甲基甲酰胺-四氢呋喃电解质溶液中的优先溶剂化现象. 红外和拉曼光谱的分析表明, Li^＋主要与DMF分子相互作用, 导致该分子的C＝O伸缩振动谱带、N—C＝O形变谱带、CH₃摇摆谱带等发生了分裂. Li^＋与其它溶剂分子的相互作用较弱, 谱带的分裂现象并不明显. Li^＋溶剂化数的计算显示, Li^＋第一溶剂化层内DMF分子的数目一般大于2, 这说明 Li^＋在混合溶剂体系内优先与DMF分子相互作用. 量子化学计算支持了这一结论.     

内含式化合物X@Al12P12的结构与稳定性研究

采用B3LYP/6-31G*方法, 对内含式化合物X@Al₁₂P₁₂ (X＝Li^0/＋, Na^0/＋, K^0/＋, Be^0/2＋, Mg^0/2＋, Ca^0/2＋, H和He)的不同对称性构型进行计算, 讨论其最稳定构型的几何参数、布居分析、偶极矩、电离势、包含能、频率、HOMO-LUMO能隙和自旋密度．发现X@Al₁₂P₁₂化合物中, 客体X＝Na^0/＋, K^0/＋, Mg和He几乎处在笼的中心, Be和Ca^0/2＋处在中心附近0.033 nm的半径内, Li^0/＋, Be^2＋, Mg^2＋和H很大程度上偏离笼的中心位置. 大部分金属内含式化合物的C₃对称性构型稳定．Li^0/＋, Be^0/2＋, Mg^2＋, Ca^2＋和H与其它离子相比更易嵌入笼内形成稳定的内含式化合物.     

X@(HAlNH)12和X(HAlNH)12 (X＝F－, Cl－, Br－, O2－, S2－, Se2－)复合物的结构和稳定性

用DFT的B3LYP方法在6-31G(d)基组的水平上, 对闭式多面体簇合物(HAlNH)₁₂及其内含式X@(HAlNH)₁₂和外接式X(HAlNH)₁₂ (X＝F^－, Cl^－, Br^－, O^2－, S^2－, Se^2－)复合物的结构进行了构型优化和能量计算, 并讨论了几何构型、自然键轨道(NBO)、振动频率、能量参数及NMR数据与结构的关系, 最后得到复合物结构的稳定性信息, 具有T_h对称性的X@(HAlNH)₁₂ (X＝F^－, Cl^－, Br^－, S^2－, Se^2－)复合物和具有C₃对称性的O^2－@(HAlNH)₁₂复合物为内含式的基态结构, 从能量角度分析, 内含式复合物比外接式复合物的结构稳定.     

X@(HAlNH)12和X(HAlNH)12 (X＝F－, Cl－, Br－, O2－, S2－, Se2－)复合物的结构和稳定性

用DFT的B3LYP方法在6-31G(d)基组的水平上, 对闭式多面体簇合物(HAlNH)₁₂及其内含式X@(HAlNH)₁₂和外接式X(HAlNH)₁₂ (X＝F^－, Cl^－, Br^－, O^2－, S^2－, Se^2－)复合物的结构进行了构型优化和能量计算, 并讨论了几何构型、自然键轨道(NBO)、振动频率、能量参数及NMR数据与结构的关系, 最后得到复合物结构的稳定性信息, 具有T_h对称性的X@(HAlNH)₁₂ (X＝F^－, Cl^－, Br^－, S^2－, Se^2－)复合物和具有C₃对称性的O^2－@(HAlNH)₁₂复合物为内含式的基态结构, 从能量角度分析, 内含式复合物比外接式复合物的结构稳定.     

BF分子X1Σ＋, A1P和B1Σ＋态的势能函数

使用SAC/SAC-CI和D95＋＋, 6-311＋＋g, 6-311＋＋g**及D95(d)基组, 分别对BF分子的基态X¹Σ^＋、第一简并激发态A¹Π和第二激发态B¹Σ^＋的平衡结构和谐振频率进行优化计算. 对所有计算结果进行比较, 得出6-311＋＋g**基组为最优基组. 运用6-311＋＋g**基组和SAC方法对基态X¹Σ^＋, SAC-CI方法对激发态A¹Π和B¹Σ^＋进行单点能扫描计算, 并用正规方程组拟合Murrell-Sorbie函数, 得到相应电子态的势能函数解析式, 由得到的势能函数计算了与X¹Σ^＋, A¹Π和B¹Σ^＋态相对应的光谱常数, 结果与实验数据较为一致.     

绿色荧光粉Ca3Y2Si3O12:Tb3+,Ce3+的制备及发光特性

采用高温固相法合成了绿色荧光粉Ca₃Y₂Si₃O₁₂:Tb³⁺。XRD检测结果显示,荧光粉主晶相为Ca₃Y₂Si₃O₁₂,属单斜晶系。荧光光谱分析表明:Ca₃Y₂Si₃O₁₂:Tb³⁺硅酸盐荧光粉可以被370nm的近紫外光激发,发射绿光,主发射峰位于490nm(⁵D₄→⁷F₆),544nm(⁵D₄→⁷F₅),585nm(⁵D₄→⁷F₄)和621nm(⁵D₄→⁷F₃)。用544nm最强峰监测,得到主激发峰位于370nm的激发光谱,此光谱覆盖了300~450nm的波长范围。研究了煅烧条件、掺杂浓度及Ce³⁺共掺杂对荧光粉发光性能的影响:在1400℃下经二次煅烧6h得到的样品的发光性能最佳,Tb³⁺离子的最佳掺杂浓度为20mol%,Ce³⁺离子共掺杂能够提高荧光粉的发光强度,其最佳掺杂量为4mol%,说明存在Ce³⁺→Tb³⁺的能量传递。     

基态N2O－的势能函数研究

以6-311＋＋G(3df, 3pd)为基函数, 采用密度泛函理论的B3LYP方法对N₂O^－分子体系的结构进行了优化计算. 结果表明N₂O^－分子最稳态为C_s构型, 电子组态为²A', 平衡核间距R_N—N＝0.11873 nm, R_N—O＝0.13012 nm, 键角∠NNO＝133.94448°, 离解能D_e＝10.3857 eV, 基态简正振动频率: 弯曲振动频率ν₁＝656.7488 cm^－1, 对称伸缩振动频率ν₂＝998.1562 cm^－1, 反对称伸缩振动频率ν₃＝1684.3093 cm^－1. 并用多体展式理论方法推导出了基态N₂O^－分子的分析势能函数, 其等值势能图准确地再现了N₂O^－分子的结构特征和离解能.     

Theoretical Investigation of the Fusion Process of Mono-Cages to Tri-Cages with CH4/C2H6 Guest Molecules in sI Hydrates

Owing to a stable and porous cage structure, natural gas hydrates can store abundant methane and serve as a potentially natural gas resource. However, the microscopic mechanism of how hydrate crystalline grows has not been fully explored, especially for the structure containing different guest molecules. Hence, we adopt density functional theory (DFT) to investigate the fusion process of structure I hydrates with CH₄/C₂H₆ guest molecules from mono-cages to triple-cages. We find that the volume of guest molecules affects the stabilities of large (5¹²6², L) and small (5¹², s) cages, which are prone to capture C₂H₆ and CH₄, respectively. Mixed double cages (small cage and large cage) with the mixed guest molecules have the highest stability and fusion energy. The triangular triple cages exhibit superior stability because of the three shared faces, and the triangular mixed triple cages (large-small-large) structure with the mixed guest molecules shows the highest stability and fusion energy in the triple-cage fusion process. These results can provide theoretical insights into the growth mechanism of hydrates with other mono/mixed guest molecules for further development and application of these substances.     

Raman spectra of gas hydrates--differences and analogies to ice 1h and (gas saturated) water

It is generally accepted that Raman spectroscopic investigations of gas hydrates provide vital information regarding the structure of the hydrate, hydrate composition and cage occupancies, but most research is focused on the vibrational spectra of the guest molecules. We show that the shape and position of the Raman signals of the host molecules (H(2)O) also contain useful additional information. In this study, Raman spectra (200-4000 cm(-1)) of (mixed) gas hydrates with variable compositions and different structures are presented. The bands in the OH stretching region (3000-3800 cm(-1)), the O-H bending region (1600-1700 cm(-1)) and the O-O hydrogen bonded stretching region (100-400 cm(-1)) are compared with the corresponding bands in Raman spectra of ice Ih and liquid water. The interpretation of the differences and similarities with respect to the crystal structure and possible interactions between guest and host molecules are presented.     

Surface-enhanced Raman spectroscopy of 12CN− and 13CN− adsorbed at silver electrodes

Measurements are reported of the surface-enhanced Raman of ¹²CN and ¹³CN (and of isotopically labelled mixtures) adsorbed at silver electrodes. The spectra are shown to arise from a complex species whose coordination number does not change with electrode potential. This species is probably a [Ag(CN₂)]^? entity having C_2v symmetry; at very negative potentials a reduced form of this complex [Ag(CN)₂]^2? coexists with the formally Ag¹ species at the surface. The shifts in band position are interpreted in terms of changes in the bond character of the adsorbed CN^? species. The spectrum of water coadsorbed with CN^? is also markedly dependent on the charge density of the adsorbed CN^? groups.     

The B 2Σ+-X 2Σ+ system of SrF: Precise spectroscopic constants from a combined fit of microwave and sub-doppler optical spectra

Doppler-free polarization spectroscopy has been used to measure 295 lines in the (0.0), (1.1) and (2.2) bands of the B ²Σ⁺-X ²Σ⁺ system of SrF. These optical data were combined with the results of separate microwave measurements of the X ²Σ⁺ state in a weighted least-squares fit. It is shown that the accuracy of spectroscopic constants of the B ²Σ⁺ state is remarkably improved by the reduction of the upper-state—lower-state correlations. A more reliable determination of the vibrational dependence of rotational and spin—rotation parameters became possible.     

The B 2Σ+-X 2Σ+ system of SrF: Precise spectroscopic constants from a combined fit of microwave and sub-doppler optical spectra

Doppler-free polarization spectroscopy has been used to measure 295 lines in the (0.0), (1.1) and (2.2) bands of the B ²Σ⁺-X ²Σ⁺ system of SrF. These optical data were combined with the results of separate microwave measurements of the X ²Σ⁺ state in a weighted least-squares fit. It is shown that the accuracy of spectroscopic constants of the B ²Σ⁺ state is remarkably improved by the reduction of the upper-state—lower-state correlations. A more reliable determination of the vibrational dependence of rotational and spin—rotation parameters became possible.     

Sorption of C6 Alkanes in Aluminophosphate Molecular Sieve, AlPO4-5

Sorption of C₆ alkanes viz.,n-hexane, 2-methylpentane, 2,2-dimethyl butane, 2,3-dimethyl butane, cyclohexane and methyl cyclopentane in AlPO₄-5 is studied and sorption capacity and thermodynamic parameters (H⁰, H, G, S and S_a) at various sorption coverage for these sorbates have been estimated. The initial heat of sorption (H⁰) is found to increase with the degree of branching in the alkane chain. The sorbate-sorbate interactions are found to be more prominent during the sorption of doubly branched alkanes and cyclic alkanes and a higher sorption capacity has been observed for cyclic alkanes. Based on the results obtained, a packing model has been proposed for various C₆ alkanes inside the AlPO₄-5 channel.     

Distribution of Butane in the Host Water Cage of Structure II Clathrate Hydrates

To understand host–guest interactions of hydrocarbon clathrate hydrates, we investigated the crystal structure of simple and binary clathrate hydrates including butane (n‐C₄H₁₀ or iso‐C₄H₁₀) as the guest. Powder X‐ray diffraction (PXRD) analysis using the information on the conformation of C₄H₁₀ molecules obtained by molecular dynamics (MD) simulations was performed. It was shown that the guest n‐C₄H₁₀ molecule tends to change to the gauche conformation within host water cages. Any distortion of the large 5¹²6⁴ cage and empty 5¹² cage for the simple iso‐C₄H₁₀ hydrate was not detected, and it was revealed that dynamic disorder of iso‐C₄H₁₀ and gauche‐nC₄H₁₀ were spherically extended within the large 5¹²6⁴ cages. It was indicated that structural isomers of hydrocarbon molecules with different van der Waals diameters are enclathrated within water cages in the same way owing to conformational change and dynamic disorder of the molecules. Furthermore, these results show that the method reported herein is applicable to structure analysis of other host–guest materials including guest molecules that could change molecular conformations.     

Radiative lifetimes of the CO a′3Σ+, b3Σ+, c3Π, d3Δ and B1Σ+ states. Absolute emission cross sections for t

Radiative lifetimes have been measured for the CO a′³Σ⁺(ν′=4–9), b³Σ⁺(ν′= 0), c³Π(ν′=0), d³Δ(ν′=1–16) and B¹Σ⁺(ν′= 0) states. Our experimental values, arranged in the same order, are 7–10 μs, 56 ns, 16 ns, 3–7.5 μs, 34 ns. Some of these values disagree with the results of previous experiments. To our opinion this is due to an incomplete identification of the emission spectrum in regions where many bands may overlap, dependent on the applied spectral resolution. For the a′Σ⁺?a³Π and d³Δ?a³Π emissions effective cross sections for quenching by CO molecules are given. In connection with the identification of the spectrum, absolute emission cross sections for electrons incident on CO have been measured for the b³Σ⁺?a³Π and c³Π?a₃Π transitions. For an electron energy, corresponding to the maximum of the excitation function we find cross sections of 5.94 (?1.2) × 10^?18 cm² and 0.630 (? 0.13) × 10^?18 cm², respectively.     

Interactions of Eu3+(aq) 7F, 5D1 and 5D0 levels with nitrate and inner-sphere (EuNO2+3)* exciplex formation

Steady-state and transient photokinetic and spectroscopic measurements on aqueous Eu(NO₃)₃ show different affinities of ⁷F, ⁵D₁ and ⁵D₀ Eu³⁺_aq towards nitrate ion. This may be rationalised by differences in the inner- and outer-shell hydration structures between ⁵D_O, ⁵D₁ Eu³⁺(_aq) and ⁷F Eu³⁺_(aq). Nitrate penetration into the inner-shell of Eu³⁺_(aq), and inner-coordination (EuNO²⁺₃)^* exciplex formation, occur solely in the long-lived ⁵D_O level of Eu³⁺_(aq).