Theoretical Investigation on Photoionization and Dissociative Photoionization of Toluene

The photoionization and dissociation photoionization of toluene have been studied using quantum chemistry methods.The geometries and frequencies of the reactants,transition states and products have been performed at B3LYP/6-311++G (d,p) level,and single-point energy calculations for all the stationary points were carried out at DFT calculations of the optimized structures with the G3B3 level.The ionization energies of toluene and the appearance energies for major fragment ions,C₇H₇⁺,C₆H₅⁺,C₅H₆⁺,C₅H₅⁺,are determined to be 8.90,11.15 or 11.03,12.72,13.69,16.28 eV,respectively,which are all in good agreement with published experimental data.With the help of available published experimental data and theoretical results,four dissociative photoionization channels have been proposed:C₇H₇⁺+H,C₆H₅⁺+CH₃,C₅H₆⁺+C₂H₂,C₅H₅⁺+C₂H₂+H.Transition structures and intermediates for those isomerization processes are determined in this work.Especially,the structures of C₅H₆⁺ and C₅H₅⁺ produced by dissociative photoionization of toluene have been defined as chain structure in this work with theoretical calculations.     

Computational, 1H NMR,and X‐ray structural studies on 1‐arylurazole tetrazane dimers

Nitrogen‐centered urazole radicals exist in equilibrium with tetrazane dimers in solution. The equilibrium established typically favors the free‐radical form. However, 1‐arylurazole radicals bearing substituents at the ortho position favor the dimeric form. We were able to determine the structure of one of the dimers (substituted at both ortho positions with methyl groups), namely 1,2‐(2,4‐dimethylphenyl)‐2‐[2‐(2,4‐dimethylphenyl)‐4‐methyl‐3,5‐dioxo‐1,2,4‐triazolidin‐1‐yl]‐4‐methyl‐1,2,4‐triazolidine‐3,5‐dione, C₂₄H₂₈N₆O₄, via X‐ray crystallography. The experimentally determined structure agreed well with the computationally obtained geometry at the B3LYP/6‐311G(d,p) level of theory. The preferred syn conformation of these 1‐arylurazole dimers results in the two aromatic rings being proximate and nearly parallel, which leads to some interesting shielding effects of certain signals in the ¹H NMR spectrum. Armed with this information, we were able to decipher the more complicated ¹H NMR spectrum obtained from a dimer that was monosubstituted at the ortho position with a methyl group.     

Numerical modeling of the formation of aerosol particles in jet engine plumes

The formation of liquid sulfate aerosols in the isobaric axisymmetric plume of a subsonic aircraft is modeled numerically. The specific features of the appearance and evolution of sulfate aerosols attributable to 2D effects, such as the parameter nonuniformity in the initial section (at the nozzle outlet), mixing of the hot engine jet with the cold air stream, and the transverse turbulent diffusion of aerosol particles and gas mixture components. The equations of gas dynamics for a turbulent axisymmetric jet, the equations of chemical kinetics, the equations for the liquid fractions (water and sulfuric acid), and the relations for the binary nucleation, condensation growth and coagulation of aerosol particles are used. The distributions of the parameters determining the formation of the aerosol phase in the exhaust plume of a B-747 aircraft are obtained and the geometry of the nucleation zone in this plume is determined.     

碳氢燃料点火燃烧的简化化学反应动力学模型

基于``准稳态'方法建立了一套复杂化学反应动力学模型简化方法和相应的软件SPARCK. 并以3种典型的碳氢燃料------甲烷、乙烯和庚烷为研究对象，从甲烷点火燃烧的GRI2.11详 细基元反应动力学模型出发简化得出了包含14个组分10步总包反应形式的简化化学反应动 力学模型，从乙烯燃烧的51组分365详细基元反应模型出发简化得出了包含20个组分16 步总包反应形式的简化化学反应动力学模型，从庚烷点火燃烧的160组分1540详细基元反 应模型出发简化得出了包含26个组分22步总包反应形式的简化化学反应动力学模型. 通过 对典型激波管试验的结果对比可以看出：得到的简化反应动力学模型能较为有效地再现 详细基元反应模型的反应机理，具有较高的计算精度. 在工程计算中有较好的应用前景.     

高质量高取向(100)面金刚石膜的可控性生长

应用微波等离子体化学气相沉积技术, 在低气压下对(100)晶面金刚石膜的表面形貌、质量、取向和生长率进行了可控性生长研究. 结果表明: 基片温度与甲烷浓度对(100)晶面金刚石膜的生长存在耦合规律. 为了获得表面形貌相似的(100)晶面金刚石膜, 在沉积过程中, 增加碳源浓度的同时需要同时升高基片温度; 当甲烷浓度为3.0%, 基片温度从740 ℃上升至1100 ℃ 的过程中, 金刚石膜的晶面取向变化可分为五个阶段, 其中当基片温度在860 ℃至930 ℃时, 很适合高取向(100)晶面金刚石膜生长; 另外, 金刚石膜的质量和生长速率分别与基片温度和甲烷浓度成正比. 为了获得高质量高取向(100)晶面金刚石膜, 应当选择合适的基片温度和甲烷浓度.     

铽掺杂羟基磷灰石的制备及其荧光特性

在室温下采用化学沉淀法制备了铽掺杂的羟基磷灰石(Tb-HAP),通过X射线衍射分析(XRD)、傅里叶变换红外光谱(FT-IR)和荧光光谱(PL)等对其结构和荧光性能进行了表征分析。XRD和FT-IR测试表明,Tb³⁺的掺杂对羟基磷灰石的结构没有显著影响。荧光光谱分析表明:在545 nm波长监测下,测得的最佳激发波长为378 nm。样品的发光强度随Tb³⁺在样品中的掺杂摩尔分数先增大后减小,在8%时发光最强。此外,Tb-HAP样品的荧光寿命随着Tb³⁺掺杂摩尔分数的增加呈现减小的趋势。     

Bond Dissociation Energies and Electronic Structures in a Series of Peroxy Radicals: A Theoretical Study

Quantum chemical calculations are performed to estimate the bond dissociation energies (BDEs) for 18 peroxy radicals. Since DFT methods are researched to have low basis sets sensitivity, these radicals are studied by utilizing the hybrid density functional theory (DFT) (B3LYP, B3P86, B3PW91 and PBE1PBE) in conjunction with the 6‐311G** basis set and the complete basis set (CBS‐Q) method. On the basis of comparisons of the computational results and the experimental values, we evaluate the effectiveness of above methods. It is demonstrated that CBS‐Q method is the best method for computing the reliable BDEs of C—OO bond, with the average absolute errors of 2.1 kcal/mol. So CBS‐Q method is suitable to predict accurate BDEs of C‐OO bond for peroxy compounds. The computational energy gaps between the HOMO and LUMO of studied compounds are almost identical from the point of view of stability and substantial HOMO‐LUMO gaps for all molecules suggest their electronic stability. In addition, substituent effect on the C—OO BDE of peroxy radicals is analyzed. It is noted that the effects of substitution on the C—OO BDE of peroxy radicals are significant. Our results will shed lights on future theoretical and experimental work.     

Opening the Pandora's jar of molecule‐to‐material conversion in chemical vapor deposition: Insights from theory

First‐principles modeling can be a powerful tool for the understanding and optimization of bottom‐up processes for nanomaterials fabrication, such as chemical vapor deposition (CVD), a key technology for the development of advanced systems and devices. Molecule‐to‐material conversion by CVD involves complex chemical phenomena, which are often obscure and still largely unexplored. A proper modeling would require high level of accuracy, large sized models and should include both temperature effects and statistical sampling of reactive events. By presenting a few selected examples, this perspective surveys such problems and discusses currently available approaches for their solution. Possible strategies for future advances in the field are also highlighted. © 2013 Wiley Periodicals, Inc.     

Synthesis of an O-acyl isopeptide by using native chemical ligation to efficiently construct a hydrophobic polypeptide

By using dimethylformamide to suppress the O-to-N acyl migration, we efficiently synthesized an O-acyl isopeptide by native chemical ligation of a peptide-thioester and a Cys-O-acyl isopeptide. The reaction mixture was then loaded onto an octadecylsilane reverse-phase HPLC column, and the isopeptide was purified by using a linear gradient of CH₃CN in 0.1% aqueous trifluoroacetic acid. The recovery rate of the O-acyl isopeptide was considerably higher than that of the corresponding native polypeptide. Synthesis of O-acyl isopeptides via native chemical ligation, with O-to-N acyl migration as the final step to give the native form, has potential as an efficient method of constructing hydrophobic polypeptides.     

IRAP: An efficient retrotransposon-based electrophoretic technique for studying genetic variability among geographical isolates of Schistosoma japonicum

In the present study, a inter-retrotransposon-amplified polymorphism (IRAP) technique, based on retrotransposons, was used to examine genetic variability among Schistosoma japonicum isolates from different provinces in mainland China. Of the 15 primers screened, 5 produced highly reproducible IRAP patterns. Using these primers, 54 discernible DNA fragments were generated with 40 (74.07%) being polymorphic, indicating considerable genetic variation among the examined S. japonicum isolates. The primer LTR-11 was found to be able to differentiate male and female parasites, producing one constant specific band for female S. japonicum isolates. The percentages of polymorphic bands (PPB) among all parasites, among isolates from mountainous provinces and among those from the lake/marshland areas were 74.07, 48.15, and 66.67%, respectively. UPGMA analysis revealed that the IRAP profiles could group S. japonicum isolates in mainland China into two clades (mountainous and lake/marshland types), and samples from the same geographical origins clustered together. These results demonstrated that the IRAP technique is suitable for studying genetic diversity and population structures, and also provides an effective technique for studying sex differentiation of S. japonicum.