Theoretical study of electric field gradients at nitrogen nuclei in HNO,CH3NO and C2H3NO

Electric field gradients (EFGs) at the nitrogen nuclei of nitroxyl, nitrosomethane and nitrosoethylene were calculated by employing the complete-active-space self-consistent field (CASSCF), internally contracted multireference configuration interaction (icMRCI) and single-configuration coupled-cluster (CC) methods with correlation-consistent basis sets at the levels of attainable accuracy. Changes in the pσ and pπ atomic orbital populations were used to rationalize the differences between the N EFG tensor components related to the nitroso compound and separate nitric oxide. Calculated ¹⁴N nuclear quadrupole coupling constants were found in reasonable accord with experimental values. Comparison of electric dipole moments and potential energy characteristics with external values served to testify to good overall quality of the wave functions used in our calculations.     

Correlation of crystal structures with electric field gradients in the fluorite- and pyrochlore-type compounds in the Gd2O3-ZrO2 system

Correlation of crystal structure with electric field gradient (EFG) in the fluorite- and pyrochlore-type compounds in the Gd₂O₃-ZrO₂ system Gd_xZr_1−xO_2−x/2 with 0.18?x?0.62 were investigated by ¹⁵⁵Gd Mössbauer spectroscopy, powder X-ray diffraction and point-charge model (PCM) calculation. An intermediate ordered pyrochlore phase forms for 0.45?x?0.55, sandwiched with a disordered fluorite phase for 0.18?x<0.45 and 0.55<x?0.62. Some ¹⁵⁵Gd Mössbauer parameters, especially the quadrupole coupling constant (e²qQ), were found to exhibit a characteristic maximum around the ideal-pyrochlore Gd₂Zr₂O₇ (x=0.50) composition. The validity of the proposed pyrochlore-based structural model was examined by comparing the experimental values of EFG at the Gd sites with those calculated by the PCM calculations.     

An ab initio calculation of 14n quadrupole coupling constants

Ab initio SCF-MO calculations of ¹⁴N quadrupole coupling constants are reported for HCN, HNC, CH₃CN, CH₃NC, NH₃, NH₂NH₂, FCN, N₂O, (CN)₂, BrCN, pyridine and pyrazine. There is excellent correlation between calculation and experiment yielding Q = 1.503 ± 0.159 × 10^?26 cm² for the ¹⁴N nuclear quadrupole moment. Dunning sp basis sets are more than adequate for such calculations, STO/4G basis sets yielding almost identical results for pyridine and pyrazine. Unsuccessful attempts were made to correlate coupling constants with electronic population analysis indices.     

Finite-field many-body perturbation theory. X. Electric field gradients and other properties of N2

Finite-field MBPT calculations have been carried out for the electric field gradient and other electric properties of the nitrogen molecule. On the basis of correlation corrections computed through the fourth order in the electron correlation perturbation the infinite order MBPT result for the electric field gradient at the nitrogen nucleus has been estimated. The corresponding result combined with the NQR coupling constant for N₂ leads to the ¹⁴N nuclear quadrupole moment of 0.0205 ± 0.0010 barn in agreement with the experimental atomic measurement and other molecular calculations. The MBPT estimate of the quadrupole moment of N₂ gives −1.107 ± 0.038 au in agreement with the most recent experimental value.     

An SCF-MS-Xα study of the bonding and nuclear quadrupole coupling in diatomic halogens and interhalogens in the ground X Σ and B Π 0 excited states

SCF-MS-Xα calculations of the electronic structure of diatomic halogens and interhalogens XY (X = I, Br, Cl; Y = I, Br, Cl, F) have been used to investigate the bonding and nuclear quadrupole coupling in these molecules. Calculations have been carried out for the ground X ¹ Σ electronic state, and for the excited B ³ Π₀ state in the case of I₂, Br₂, ICl and IBr. Good agreement (to within 10% in most cases) is obtained between the calculated and observed nuclear quadrupole coupling constants for the molecules in the ground state. For the excited state the agreement is not as good, but the calculation does reproduce the observed decrease in the coupling constants to less than one quarter of their ground state values, and analysis of the contributions to the field gradients clearly shows the reasons for this. The electric dipole moments and electric quadrupole moments of the molecules have also been calculated. However, these prove to be much more strongly dependent on the variables used in the calculation (atomic sphere radii, inclusion of d orbitals). The results of the calculations have also been used to test some of the assumptions made in the Townes and Dailey method of analysis of nuclear quadrupole coupling data.     

Electric field gradients in the ionic crystals NaNO2, NaBF4, NaNO3, and Ba(NO3)2

The electric field gradients (EFG) at the sites of the cations and the “central” atoms of the anions in the ionic crystals NaNO₂, NaBF₄, NaNO₃ and Ba(NO₃)₂ are calculated by a method based on a combination of the semi-empirical INDO method for the charge distribution and the intramolecular EFG with a lattice summation in the framework of the extended multipole model. At some lattice sites the contribution of the induced dipole and quadrupole moments to the EFG is comparable with the contribution of the point charges. The charge distribution within the molecular ions is found by adjusting either the calculated asymmetry parameter η or the z-component of the EFG to the experimental value deduced from nuclear quadrupole coupling constants. These charge distributions are in good agreement with those gained from INDO calculations. The calculated and experimental quadrupole coupling constants of nuclei in anions and cations are compared.     

A CASSCF/icMRCI study of the electric field gradient in low-lying electronic states of N2/N2

The electric field gradients (EFG’s) at the nucleus are calculated as a function of internuclear separation in the X²Σ_g⁺ and B²Σ_u⁺ electronic states of the nitrogen molecule cation using the internally contracted multireference configuration interaction (icMRCI) method. The EFG’s and potential energy functions (PEF’s) are used to estimate the ¹⁴N nuclear quadrupole coupling constants (NQCC’s) in the two electronic states as functions of vibrational and end-over-end rotational quantum numbers. The dependences of the computed constants on the basis set and reference configuration space are investigated. Since no counterpart for comparison of the calculated NQCC’s exists, the N₂⁺ results are supported by analogous calculations on the X¹Σ_g⁺ and A³Σ_u⁺ states of N₂, for which established data are available. The overall good quality of the icMRCI wave functions is further corroborated by a favorable agreement of spectroscopic constants derived from the corresponding PEF’s and experimental data. Variations of the EFG with internuclear separation are explained in terms of wave function composition, and used for gaining specific insight into the chemical bonding in N₂⁺ and N₂.     

双帽Keggin型杂多阴离子[H4As3Mo12O40]-和Keggin型杂多酸H3PM12O40 (M＝Mo, W)质子化的DFT研究

选用B3LYP方法在LanL2MB水平下, 对双帽α-Keggin型杂多阴离子[H₄As₃Mo₁₂O₄₀]^-的电子结构和质子的定位进行了密度泛函理论(DFT)研究. 结果表明, 双帽的形成大大影响了杂多阴离子[As₃Mo₁₂O₄₀]^5－的电子结构和性质, NBO分析显示参与成帽的三桥氧上的电子密度比双桥氧上的要大, 简单地从电荷密度来看, 质子将首先在三桥氧上定域成键, 但通过比较质子定域在几种桥氧上质子化稳定化能的大小, 发现[H₄As₃Mo₁₂O₄₀]^-中的四个质子将在八个双桥氧中的其中四个氧原子上定位, 而不是如文献中报道的在四个三桥氧上定域成键. 对杂多酸H₃PM₁₂O₄₀ (M＝Mo, W)中质子的定位也进行了理论计算并与文献进行了比较, 结果显示, H₃PMo₁₂O₄₀中质子是定位在双桥氧上; 而H₃PW₁₂O₄₀中质子将优先在双桥氧上定位, 但也可在端氧上定位; 这一结果与文献报道的相一致.     

α-Fe2O3/SiO2纳米颗粒混合体系表面的酸碱性质及其对重金属离子的吸附行为

以Fe(NO₃)₃·9H₂O和正硅酸乙酯(TEOS)为原料, 通过溶胶-凝胶法和辅助模板法分别制备了纳米α-Fe₂O₃和SiO₂, 并对所合成样品进行了粉末X射线衍射(XRD)和BET表征. 使用自动电位滴定仪测定了α-Fe₂O₃/SiO₂纳米颗粒混合体系的表面酸碱性质. 研究了在不同pH下α-Fe₂O₃/SiO₂混合体系对Cu²⁺、Pb²⁺、Zn²⁺离子的吸附行为. 基于上述实验数据, 用WinSGW软件计算了α-Fe₂O₃/SiO₂混合体系表面酸碱配位常数, 并得出结论: α-Fe₂O₃/SiO₂混合体系表面反应为单一脱质子反应≡XOH ⇔ ≡XO^-+ H⁺(lg K = -8.19±0.15), 明显区别于同时具有加质子和脱质子反应的α-Fe₂O₃/SiO₂/γ-Al₂O₃, α-Fe₂O₃/γ-Al₂O₃和SiO₂/γ-Al₂O₃等纳米颗粒混合体系. 在此基础上拟合得到α-Fe₂O₃/SiO₂混合体系吸附重金属离子Cu²⁺、Pb²⁺、Zn²⁺的表面络合反应平衡常数分别为:
≡XOH + M²⁺ ⇔ ≡XOM⁺+ H⁺ [lg K = -3.1, -3.6, -3.8 (M = Cu, Pb, Zn)].
≡XOH＋M²⁺＋H₂O ⇔≡XOMOH＋2H⁺[lg K = -8.8, -8.0, -10.5 (M = Cu, Pb, Zn)]     

“NMR invisible” aluminum species in dealuminated mordenite zeolite: a1H/27 AI TRAPDOR NMR study

Various kinds of aluminum species in dealuminated mordenite were investigated in detail, and the quadrupole coupling constants (QCCs) for aluminum atoms associated with these species were obtained by means of the newly introduced¹H/²⁷ AI TRAPWR method as well as²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR). QCC values of 11.3, 15.3, 13.3 and (14.0± 0.6) MHz were determined from the TRAPDOR profiles for Lewis acid sites, Bronsted acid sites (SiOHAl) and two kinds of non-framework aluminum species Al(OH) _n , respectively. The source of the “invisible Al” is discussed on the basis of the NMR experimental results.     

层状Li(Ni1-xCox)O2结构研究

0引言层状钴酸锂是目前锂离子电池主要正极材料,但是,随着锂离子电池的广泛使用,急需比钴酸锂价格低和来源广泛的正极材料,层状锰酸锂和层状镍酸锂受到重视。由于锰氧化物存在有J-T效应,因此,严格意义上的层状锰酸锂的制备极其困难。制备层状镍酸锂也非常困难,高温反应极易生成Li1-xNi1 xO2,具有此种结构的镍酸锂存在严重首次能量衰减和循环性能下降的缺点。采用其他元素掺杂镍酸锂克服其缺点的研究已经很多,其中钴掺杂镍酸锂由于显示了良好的效果而被认为是最有希望替代钴酸锂的锂离子电池正极材料。有关层状镍钴酸锂的研究很多,但不少的…     

Density functional theory and Hartree–Fock-density functional theory calculations of O, S, and Ge quadrupole coupling constants

The performance of several density functional theory and Hartree–Fock density functional theory methods in conjunction with Pople type bases for the calculation of ¹⁷O, ³³S, and ⁷³Ge quadrupole coupling constants in gaseous state molecules was investigated.Assessment of the several models was made by linear regression analysis of the calculated gradient of the molecular electric field versus the experimental nuclear quadrupole coupling constant (NQCCs). Calculations for oxygen on six molecules with the B3LYP/6-311++G(3df,3p) model yield a residual standard deviation of 0.057 MHz (1.4%); for sulfur on 12 molecules with the B3LYP/6-311G(3df,3p) model, 0.42 MHz (1.8%); and for germanium on nine molecules with the B3P86/6-311G(2d) model, 0.83 MHz (1.0%).In the case of germyl acetylene, our calculations indicate that the experimental NQCC reported some time ago by Thomas and Laurie [J. Chem. Phys. 44 (1966) 2602] was incorrectly assigned with respect to algebraic sign.Predictions are made of the ¹⁷O and ³³S NQCCs in furan, 4H-pyran-4-one, 4H-pyran-4-thione, and 4H-thiapyran-4-thione; and of the ⁷³Ge NQCC in germyl bromide.     

系列硅铝比纳米薄层ZSM-5分子筛的合成和表征

以自制不对称双子季铵盐表面活性剂为模板, 在水热合成体系中控制合成系列硅铝比纳米薄层ZSM-5分子筛.采用X射线衍射(XRD)、N₂吸附-脱附、X射线荧光光谱(XRF)、扫描电镜(SEM)和²⁷Al魔角旋转核磁共振(²⁷Al MAS-NMR)对合成的样品进行了表征. 详细研究了晶化温度、晶化时间、结构导向剂(SDA)用量、碱度等对合成的影响和纳米薄层ZSM-5分子筛的形成过程. 结果表明: 分子筛硅铝比越高, 结构导向剂用量越大, 所需的晶化时间越短; 晶化温度越高, 晶化时间越短; 且不同硅铝比纳米薄层ZSM-5分子筛的形貌规整度、比表面积和介孔/微孔孔容比例随着硅铝比而变化.     

CO LMR spectrum of14N16O and its analysis with spectra of14N17O and14N18O

LMR spectra for v=1←0 transitions of¹⁴N¹⁶O in X²II_{1/2, 3/2} states were observed at 5.6 μm and 5.4 μm of CO laser. Introducing the advanced isotopic molecular constant scaling function to Hund’s case (a) diatomic structure model, these spectra were analyzed and fitted together with all reliable previous spectral data of¹⁴N¹⁶O as well as¹⁴N¹⁷O and¹⁴N¹⁸O. A full set of precise molecular parameters and their vibrational dependencies have been determined with much higher precision (1–2 orders for most parameters). Many of them have been obtained for the first time. Using isotopic scaling function, the molecular constants of¹⁴N¹⁷O and¹⁴N¹⁸O were deduced.     

B24N24 nanocages: a GIAO density functional theory study of 14N and 11B nuclear magnetic shielding and electric field gradient tensors

Abstract  

Density functional theory (DFT) calculations were performed to determine boron-11 and nitrogen-14 nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) spectroscopy parameters in the three most stable B₂₄N₂₄ fullerenes for the first time. The considered samples were first allowed to relax entirely, and then the NMR and NQR calculations were performed on the geometrically optimized models. The calculations of the ¹¹B and ¹⁴N nuclear magnetic shielding tensors and electric field gradient tensors employed the Gaussian 98 software implementation of the gauge-including atomic orbital (GIAO) method using the Becke3, Lee-Yang-Parr (B3LYP) DFT level and 6-311G** and 6-311++G** standard basis sets in each of the three optimized forms, and converted the results to experimentally measurable NMR parameters.The calculated NMR chemical shieldings of the three cages show significant differences, providing a way to identify these clusters. The evaluated NQR parameters of the ¹¹B and ¹⁴N nuclei in the clusters are also reported and discussed.     

La7O6(BO3)(PO4)2:Eu3+/Tb3+荧光材料的制备及其光致发光性能

采用优化的高温固相方法制备了稀土离子Eu³⁺和Tb³⁺掺杂的La₇O₆（BO₃）（PO₄）₂系荧光材料,并对其物相行为、晶体结构、光致发光性能和热稳定性进行了详细研究。结果表明,La₇O₆（BO₃）（PO₄）₂：Eu³⁺材料在紫外光激发下能够发射出红光,发射光谱中最强发射峰位于616 nm处,为⁵D₀→⁷F₂特征能级跃迁,Eu³⁺的最优掺杂浓度为0.08,对应的CIE坐标为（0.610 2,0.382 3）;La₇O₆（BO₃）（PO₄）₂：Tb³⁺材料在紫外光激发下能够发射出绿光,发射光谱中最强发射峰位于544 nm处,对应Tb³⁺的⁵D₄→⁷F₅能级跃迁,Tb³⁺离子的最优掺杂浓度为0.15,对应的CIE坐标为（0.317 7,0.535 2）。此外,对2种材料的变温光谱分析发现Eu³⁺和Tb³⁺掺杂的La₇O₆（BO₃）（PO₄）₂荧光材料均具有良好的热稳定性。     

g-C3N4/Bi2O2CO32D纳米片复合材料的制备及可见光催化性能研究

采用自组装和化学沉淀法分别制得两种可见光驱动复合材料石墨相氮化碳/碳酸氧铋(g-C_3N_4/Bi_2O_2CO_3).采用X射线衍射光谱(XRD),紫外可见光谱、扫描电镜(SEM)、N_2吸附、电化学阻抗谱(EIS)和X射线光电子能谱(XPS)等分析手段对制备的催化剂进行了表征.结果表明,制备方法对纳米复合材料的晶相、形态及光学性能没有影响,但是影响g-C_3N_4和Bi_2O_2CO_3之间的相互作用力,导致光生电子-空穴对的分离速率存在显著差异.以可见光驱动苯酚和罗丹明B的降解实验为探针反应检测催化剂的光催化性能.实验结果表明自组装法得到的异质结催化剂中相互作用力更强,催化效果最高.O_2-是罗丹明B降解反应的主要活性物种,染料的光敏化、Bi_2O_2CO_3与g-C_3N_4综合效应,导致光生载流子电荷分离效率更高.     

Conversion of NO in NO/N2, NO/O2/N2, NO/C2H4/N2 and NO/C2H4/O2/N2 Systems by Dielectric Barrier Discharge Plasmas

An experimental study on the conversion of NO in the NO/N₂, NO/O₂/N₂, NO/C₂H₄/N₂ and NO/C₂H₄/O₂/N₂ systems has been carried out using dielectric barrier discharge (DBD) plasmas at atmospheric pressure. In the NO/N₂ system, NO decomposition to N₂ and O₂ is the dominating reaction; NO conversion to NO₂ is less significant. O₂ produced from NO decomposition was detected by an on-line mass spectrometer. With the increase of NO initial concentration, the concentration of O₂ produced decreases at 298 K, but slightly increases at 523 K. In the NO/O₂/N₂ system, NO is mainly oxidized to NO₂, but NO conversion becomes very low at 523 K and over 1.6% of O₂. In the NO/C₂H₄/N₂ system, NO is reduced to N₂ with about the same NO conversion as that in the NO/N₂ system but without NO₂ formation. In the NO/C₂H₄/O₂/N₂ system, the oxidation of NO to NO₂ is dramatically promoted. At 523 K, with the increase of the energy density, NO conversion increases rapidly first, and then almost stabilizes at 93–91% of NO conversion with 61–55% of NO₂ selectivity in the energy density range of 317–550 J L⁻¹. It finally decreases gradually at high energy density. A negligible amount of N₂O is formed in the above four systems. Of the four systems studied, NO conversion and NO₂ selectivity of the NO/C₂H₄/O₂/N₂ system are the highest, and NO/O₂/C₂H₄/N₂ system has the lowest electrical energy consumption per NO molecule converted.     

Electronic structure of BeH2

Nonorthogonal single‐configuration and multiconfiguration ab initio calculations are carried out on the BeH₂ molecule in its equilibrium (D_∞h) geometry, using a highly optimized even‐tempered Slater‐type orbital (STO) basis set. The results are used as a basis for a discussion of the electronic structure of the molecule in modern‐VB terms. A value of R_e = 1.329 Å is obtained. Values are also obtained for the symmetric‐stretch harmonic frequency (2053 cm^?1), electric quadrupole moment (?5.60 Buckingham), and nuclear quadrupole coupling constants (?3.59 MHz for ⁹Be and 0.0915 MHz for ²H). © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Vibrational frequencies and force constants of N2O4 in complexes with molecules of different solvents determined by Raman spectra andAb initio calculation

The Raman spectra of N₂O₄ solutions in organic solvents have been recorded. The frequencies ofv ₁,v ₂, andv ₃ bands of N₂O₄ increase with increasing solvent electron-donor properties. Especially large changes ofv ₃ N-N stretching band have been observed (254.5 cm^–1 in n-hexane, 276.5 cm^–1 in 1,4-dioxane). The ab initio calculations have shown that the interaction between N₂O₄ and electron-donor molecules causes an increase of N-N and N-O stretching and O-N-O bending force constants of N₂O₄ in agreement with the results of Raman study.