C60(NO2)2: Quantum-Chemical Evaluations of Structure,Energetics, and Vibrational Spectra

Abstract

The complete PM3 structural optimizations are reported for all 23 positional isomers of C₆₀(NO₂)₂ and interesting symmetry reductions are found. There are two low energy structures while all the remaining species are separated by more than 10 kcal/mol from the computed ground state. In the ground state the two nitro groups are placed in para position on one hexagon. The next lowest structure is produced by addition to one 6/6 (double) bond of the cage. The species highest in energy are separated by more than 50 kcal/mol from the ground state. IR vibrational spectra are also predicted for the low-energy structures.     

Thermal Transformation of Ring-Opened [2 2] C60 Dimer into a Wide-Bridged C120 Isomer. A Computational Evaluation of Fulvalene-Naphthalene Rearrangements

As a continuation of the studies on thermal transformation of the [2+2] C₆₀ dimer (1), the consequence of the pyracylene-rearrangement-like valence isomerization of the fulvalene partial structure at the bridge of the ring-opened product from 1, namely 2, was searched by dynamic reaction coordinate /AM1 semiempirical MO calculations. It is predicted that the fulvalene bridge of 2 rearranges into naphthalene partial structure by the concerted 'in-plane' mechanism to give a wide-bridged C₁₂₀ intermediate having twenty five-membered rings and two ten-membered rings (3). The computed energy of activation (145 kcal/mol) is 40 kcal/mol lower than those computed for pyracylene rearrangements. In contrast, the recently reported analogous rearrangement of indigo (13) to dibenzonaphthyridindione (14) is computed to occur by the stepwise 'sp³' mechanism.     

AMI Computations on C59: Significant Eight- and Nine-Membered Rings

C₅₉ is computed by the AMI method as a particular, experimentally known odd fullerene, 19 isomers being treated. New rules are reported for the pentagon/hexagon pattern, and structures with other types of rings are considered, too. A part of the isomers is derived from the lowest known isomer of C₅₈- The supposed ground-state structure of C₅₉ contains an eight-membered ring, while the next lowest one possesses a nine-membered ring. The C₅₉ ground state exceeds C₆₀ in heat of formation per particle by about 10.4 kJ/mol/atom. The ground-state species should prevail in the C₅₉ equilibrium isomeric mixture even at high temperatures.     

Penultimate Intermediates to C60 and C70

Penultimate intermediates leading to C₆₀ and C₇₀ fullerenes contain one or two pairs of pentalene units and 32 to 55 kcal/mol less stable than the final products. Energy barriers of pyracylene rearrangements from these intermediates to the final products are computed to be 118 to 125 kcal/mol in height by MOPAC/AM1, which are comparable to those of preceding steps in the Stone-Wales rearrangement cascade.     

Cyclic and Linear Structures of C13: A Computational Study

Recently, a linear structure of C₁₃ was observed and its infrared spectrum recorded. Computations of the linear and cyclic structures of C₁₃ are thus presented. The computations are performed at ab initio level using the standard 6-31G* basis set. Electron correlation is treated by density functional theory (Becke3LYP) and perturbation treatment (MP2=FC). With the density-functional approach the standard 6-311G* and 6-311G(2d,p) basis sets are applied, too. In all the treatments the cyclic structure (C_2v symmetry) is located about 90 kJ/mol below the linear form (D_∞h symmetry), while a tricyclic structure is considerably higher in energy (about 280 kJ/mol above the monocyclic species). Even at high temperatures the linear form represents less than 10% of the equilibrium isomeric mixture. Computed IR spectra are also reported. The stability evaluation corresponds to the findings of ion chromatography.     

One-, Two- and Three-Dimensional Structures of C20

The aggregates C₂₀ have been studied by the AM1 quantum-chemical method and at least three different local energy minima found. The located planar cyclic ground state exhibits C_10h symmetry, being followed by two triplet linear structures, a spheroidal C₁ structure, and a bowl-shaped C_5v structure.     

Two Isomers of C60F48: Computed Inter-isomeric Equilibrium

C₆₀F₄₈ has been known to exist in two isomeric forms of D₃ and S₆ symmetries. However, the quantum-chemical calculations have not agreed on their stability order though a near-isoenergetic picture is otherwise always encountered. In order to clarify the situation, the entropy effects are evaluated for synthetic temperatures of about 500K. The entropy evaluations suggest that the D₃ isomer should be more stable in the potential energy by 2.05-2.55 kcal/mol (to which term the ab initio data are closer than the semiempirical ones).     

Average Bond Dissociation Energies of Fullerene

Average carbon-carbon bond dissociation energy of buckminsterfullerene C₆₀ is estimated to be 106.87 kcal/mol by using experimentally determined thermochemical data. With a few assumptions this value was converted to the following bond-specific dissociation energies for fullerenes in general: 112.04 kcal/mol for 6/6 type bond, and 104.88 for 5/6 type. Similarly an average value of 60.34 kcal/mol was assigned to 5/5 type bond.     

Competition between ferromagnetic and antiferromagnetic interaction in monoclinic LiMnO2

The electronic and magnetic structures of monoclinic LiMnO₂ are investigated by first-principles calculations with spin-polarized generalized gradient approximation. It is found that the Mn³⁺ ion is in the high-spin state. The ground state is found to be an insulating state with competing ferromagnetic and antiferromagnetic interaction, and it is this competition that results in the spin-glass behavior observed in monoclinic LiMnO₂.     

A first principles study of small Cun clusters based on local-density and generalized-gradient approximations to density functional theory

Neutral and anionic Cu_n clusters (Cu₂, Cu₃, Cu₆ and Cu₇⁻) are studied within density functional theory via (a) the local-density approximation (LDA) and (b) the generalized-gradient approximation (GGA) of Perdew and Wang (GGA-PW) for exchange and correlation. GGA reduces by ˜20% the binding energies, while the bond lengths are increased by ˜3–4%. The different levels of GGA approximation, involving optimization of the electronic density and/or of the geometry, are shown in detail. In the case of Cu₆ the GGA configurational ground state is a planar structure of D_3h symmetry. This result differs from the one obtained by LDA, where the three different isomers (one two-dimensional and two three-dimensional) were found to lie within 0.04 eV.     

Ab initio calculation on fullerene C32 and Its Derivative

In this paper, we studied the equilibrium geometries, the electronic structures and the binding energies of fullerene C₃₂ as well as its hydrogenates and fluorides interactions by the SCF Hartree-Fock calculations using the latest version of GAMESS of ab initio programs. The fullerene C₃₂ is found to have a ¹A₂' closed-shell ground state in D_3d symmetry or a ¹E_U singlet state in D_3h symmetry. It is predicted to be easy to add some hydrogen or fluorine atoms to the C₃₂ cage and to produce a series of derivatives C₃₂H_2n,C₃₂F_2n (n=l, 3, 6), in which C₃₂H₂,C₃₂F₂ (D_3d), C₃₂H₆^a,C₃₂F₆^c(D_3h) are more stable. We suggest that this implies that the vertex of triplet pentagons of the C₃₂ cage is an activation site for addition.     

VO2(B)/ZnO异质复合纳米棒结构的室温NH3敏感性能研究

以VO₂(B)纳米棒为内核, 利用液相生长法制备了VO₂(B)/ZnO异质复合纳米棒, 研究了ZnO生长溶液浓度对复合结构微观形貌和气敏性能的影响规律。采用扫描电子显微镜和X射线衍射仪对复合结构样品的微观形貌和结晶取向进行表征, 并测试了复合结构对NH₃的敏感性能。实验结果表明, 随着ZnO种子液浓度的增大, ZnO逐渐由纳米颗粒生长为纳米棒结构, 当ZnO种子液浓度为0.01 mol/L时, ZnO呈棒状沿径向发散生长在VO₂(B)纳米棒表面, 形成树枝状VO₂(B)/ZnO异质复合纳米棒结构, 这一结构在室温下表现出对NH₃的高灵敏度和突出的选择性, 其灵敏度最大可达5.6, 对NH₃的响应时间最短仅为2 s。在室温下表现出的优良NH₃敏感性能, 主要与高密度的VO₂(B)/ZnO异质结和树枝状结构有关。研究结果为低功耗高灵敏度NH₃气敏传感器的研制提供了重要依据。     

Densification and Grain-Growth Behavior of Various Amounts of SiO2 Doped 8YSCZ/SiO2 Composites

The effect of SiO₂ addition on densification and grain-growth behavior of 8YSCZ/SiO₂ composites was investigated using high purity 8 mol% yttria-stabilized cubic zirconia powders (8YSCZ) doped with 0, 1, 5, 10 wt% SiO₂. The specimens were sintered at 1400°C for 1 hour. It was seen that the sintered density increased with SiO₂ content up to 1 wt% and further increase in SiO₂ content led to a decrease in density. The enhanced density with increasing SiO₂ content up to 1 wt% could be mainly attributable to liquid phase sintering. For grain growth measurements, the specimens sintered at 1400°C were annealed at 1400, 1500, and 1600°C for 10, 50, and 100 hours. The experimental results showed that the grain growth in 8YSCZ/SiO₂ composites occurred more slowly than that in undoped 8YSCZ. Also, the grain growth rate decreased with increasing SiO₂ content. The grain growth exponent value and the activation energy for undoped 8YSCZ were found to be 2 and 289 kJ/mol, respectively. The addition of SiO₂ raised the grain growth exponent value to 3, and activation energy for the grain growth process was increased from 289 to 420 kJ/mol for the addition of SiO₂ from 0 to 10 wt%.     

New transparent conducting MgIn2O4---Zn2In2O5 thin films prepared by magnetron sputtering

New materials for a transparent conducting oxide film are demonstrated. Highly transparent Zn₂In₂O₅ films with a resistivity of 3.9 × 10⁻⁴ Ω cm were prepared on substrates at room temperature using a pseudobinary compound powder target composed of ZnO (50 mol.%) and In₂O₃ (50 mol.%) by r.f. magnetron sputtering. MgIn₂O₄---Zn₂In₂O₅ films were prepared using MgIn₂O₄ targets with a ZnO content of 0–100 wt.%. The resistivity of the deposited films gradually decreased from 2 × 10⁻³ to 3.9 × 10⁻⁴ Ω cm as the Zn/(Mg + Zn) atomic ratio introduced into the films was increased. The greatest transparency was obtained in a MgIn₂O₄ film. The optical absorption edge of the films decreased as the Zn/(Mg + Zn) atomic ratio was increased, corresponding to the bandgap energy of their materials. It was found that the resistance of the undoped Zn₂In₂O₅ films was more stable than either the undoped MgIn₂O₄, ZnO or In₂O₃ films in oxidizing environments at high temperatures.     

Quantum Chemical ab initio Investigations of Non-Covalent Bonding Derivatives of Fullerene C60 and Li Atom or Cs2, C6H6 Molecules

Abstract

Quantum chemical ab initio investigations of the stability of the non-covalent fullerene complexes: C₆₀ molecule + Li atom, two C₆₀, two C₆₀ + CS₂, C₆₀ + CS₂, C₆₀ + C₆H₆ were performed using Hartree-Fock (HF) and Density Functional Theory (DFT) methods in various basis sets. The inclusion of electron correlation effect calculated by using DFT B3PW91 model during the optimization of Li atom position above hexagonal of C₆₀ gives the smaller distance from the centre of C₆₀ equal to 7.75 Å and large positive energy of formation equal to 4.452 kcal/mol in comparison with HF calculated distance 8.39 Å and energy of formation 1.810 kcal/mol. The positive energy of formation equal to 0.483 kcal/mol for optimized complex two C₆₀ + one CS₂ was found by HF. The presence of CS₂ molecule stabilises this complex with the energy equal to 0.281 kcal/mol. Complexes: C₆₀ + CS₂, C₆₀ + C₆H₆ do not possess the positive energy of formation.     

Ag与Ag2O协同增强TiO2光催化制氢性能的研究

本研究采用两步法制备了电子助剂Ag和界面活性位点Ag₂O共修饰的高效TiO₂光催化剂(TiO₂/Ag-Ag₂O): 首先用光沉积法将Ag负载在TiO₂表面(TiO₂/Ag), 再经过低温煅烧法使部分Ag原位生成Ag₂O。紫外光照射TiO₂时, 激发产生的电子被助剂Ag捕获后快速传输到Ag₂O上, 电子把Ag₂O界面产氢活性位点从溶液中所捕获的氢离子还原成氢气, Ag和Ag₂O的协同作用加快了TiO₂上光生电子的转移和界面产氢反应, 从而提高了TiO₂/Ag-Ag₂O制氢性能。在300 ℃煅烧温度下制备的TiO₂/Ag-Ag₂O光催化剂制氢速率最高, 达到75.20 μmol/h, 分别是TiO₂(3.59 μmol/h)和TiO₂/Ag(41.13 μmol/h)的21.0倍和1.8倍。本研究为光催化制氢材料的设计和制备提供了有益的参考。     

CHEMICAL VAPOR DEPOSITION OF TiB2 FOR TiN-TiB2 LAMINAR COMPOSITES

TiB₂ is a material with very interesting properties with respect to erosion and corrosion resistance. Deposition on metallic substrates using TiCI₄, BBr₃ or BCI₃ and H₂ at temperatures around 900° C results in coronation of the substrate, which is most severe when using BBr₃. Therefore, a TiN diffusion barrier is applied. Here we discuss the deposition of TiB₂ using BCI₃ on molybdenum and TiN and compare the results with those of the thermodynamically more favorable reaction with BBr₃. Smooth TiB₂ layers are formed when using BCI₃, with faceting occurring above 900° C. The morphology seems to be independent of the BCI₃/TiCl₄ ratio in the gas phase for values between 0·5 and 4. With an excess of boron in the gas phase - BCI₃/TiCl₄ = 8, depletion occurs already at 800° C. An apparent activation energy of 210 KJ/mol has been determined for a stoichiometric gas phase with BCl₃/TiCI₄ = 2. When the supply of boron is limiting - BCl₃/TiCl₄ = 0·5, the activation energy is 120 KJ/mol.     

典型换能元与点火药剂匹配试验研究

选用桥丝（BW）与金属薄膜（MF）两种镍铬合金换能元,以及Pb(SCN)₂/KClO₃与Zr/Pb₃O₄两种点火药剂,分别制备了4种不同的点火元件。点火元件与5.8系发射药制成药包,并在密闭爆发器中点燃,获得相应的压力=时间曲线,以此探讨不同点火药与典型换能元的匹配情况。其中,涂覆有4.8 mg Pb(SCN)₂/KClO₃的金属薄膜点火头增压速率为80.84 MPa/s,而涂有相同质量药剂的桥丝点火头增压速率仅为68.15 MPa/s。结合高速摄影图像与理论分析认为:换能元的电热转换效率可以在较大程度上影响点火药剂的发火状态;金属薄膜换能元由于具有较为集中的发火区域,因此点火能力相较于桥丝换能元更加稳定;Pb(SCN)₂/KClO₃药剂的发火状态也比Zr/Pb₃O₄药剂稳定。