二硅烯异构化反应的理论研究, 从头等水平上的动力学, 热力学分析

本文在从头算水平上计算了二硅烯HXSi-SiH2(X=H,D)异构化反应的反应物、产物及过渡态构型的能量、谐振动频率和反应活化能等,又计算了反应的热力学函数变化, 平衡常数及速率常数, 结果表明,该异构化反应是放热的, 且可自发进行, 结论与Newman的实验事实相符合, 值得注意的是, 零点能校正对该异构化反应的计算有改进。     

宽广温度范围的水离子积计算公式

宽广温度范围的水离子积是在理论上和实际应用上涉及面很广的重要物理化学性质之一.傅培鑫,Quist及Marshall等在总结实验数据的基础上提出了相应的计算水离子积的经验公式;Taylor还用热力学方法进行了计算.在饱和蒸气压及0～800℃范围内,以Marshall-Franck的经验公式准确度为最高,并由国际蒸气性质协会(IAPA)于1980年公布为计算宽广温度范围的水离子积公式.但是在温度较高(200～300℃)时,此公式的计算值与实验值之间的误差随温度升高而逐渐增大,平均误差为0.033pK_w单位.     

按非刚性转子模型计算NF3和环氧乙烷的光谱熵

NF_3和环氧乙烷(C_2H_4O)作为推进剂,曾由Sundaram按刚性转子-谐振子模型计算了其光谱熵.但由于忽略了离心力的影响,必然致使计算结果偏低(尤其在高温下).本文按Kivelson等给出的离心力校正参数τ值与离心力伸长常数D_J、D_(JK)和D_K间的关系式,由微波谱给出的数据计算了C_2H_4O的离心伸长常数(表1).改按非刚性转子—谐振子模型,采用直接加和法重新精确计算转动、振动配分函数,进而在100～2000K范围内计算了NF_3和C_2H_4O的光谱熵(表2).比较了所得结果与Sundaram的计算值     

Effect of branching on the thermal properties of novel branched poly(4‐ethyleneoxy benzoate)

Poly(4‐ethyleneoxy benzoate) (PEOB) was synthesized by the self‐condensation of ethyl 4‐(2‐hydroxyethoxy) benzoate (E4HEB) under transesterification conditions. Branched PEOB was prepared by the condensation of E4HEB with an AB₂ monomer, ethyl 3,5‐bis(2‐hydroxyethoxy) benzoate (EBHEB), under similar conditions. Varying amounts of branching (0–50%) were introduced into the linear polymer by changes in the composition of the comonomers in the feed. The solution viscosity of the polymers indicated that they had reasonable molecular weights; the extent of branching in these copolymers was established from their ¹H NMR spectra. Differential scanning calorimetry studies indicated that, as expected, the introduction of branching drastically affected the percent crystallinity of the copolymers (as seen from their ΔH_m, the enthalpy of melting), and when the extent of the incorporation of the AB₂ monomer exceeded 10 mol %, the copolymers were completely amorphous. The melting temperatures of the copolymers decreased with an increase in the branching content, whereas the peak crystallization temperature in quenched (amorphous) samples followed the exactly opposite trend. The glass‐transition temperatures (T_g) of the branched copolymers first decreased at low extents of branching, passed through a minimum, and then increased to attain the T_g of the pure hyperbranched polymer of EBHEB. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 261–268, 2000     

电子转移反应O~2+O~2^.^-→O~2^.^-+O~2的从头算研究

利用abinitio方法,在UHF,UMP2及不同基组3-21G,6-31G^*,6-311+G^*和UMP2(full)/6-311+G^*水平上,研究了O~2/O~2^.^-自交换电子转移反应。优化了电子转移前后反应物和产物的结构,研究了体系能量的变化,计算了自交换电子转移反应的内重组能。对UHF方法和UMP2方法的计算结果进行了比较,并与实验结果进行了对照。结果表明UHF方法由于没有考虑组态相互作用,计算结果存在较大偏差,UMP2(full)/6-311+G^*水平上的计算结果与实验值吻合较好。在UMP2(full)/6-311+G^*水平上计算了气相自交换电子转移反应速率常数。在优化了电子转移复合物结构的基础上考虑了溶剂效应的影响,计算了水溶液中的溶剂重组能。研究结果表明O~2/O~2^.^-体系电子转移反应的活化能主要来源于溶剂重组能的贡献。最后计算了该反应在水溶液中的反应速率常数。理论计算结果与实验值吻合得很好。     

甲基环丙烷卡宾重排反应机理的探讨

本文用HF/STO-3G解析梯度方法计算了甲基环丙烷卡宾重排反应的8个构型,它们代表4个反应类型.计算结果表明,甲基的H原子对卡宾碳的1,3迁移遵从端端告拢机理.环丙烷上的H原子1,2迁移活性遵从夹有相似文献   

A new sequence isomer of AB‐polybenzimidazole for high‐temperature PEM fuel cells

A new sequence isomer of AB‐polybenzimidazole (AB‐PBI) was developed as a candidate for high‐temperature polymer electrolyte membrane fuel cells. A diacid monomer, 2,2′‐bisbenzimidazole‐5,5′‐dicarboxylic acid, was synthesized and polymerized with 3,3′,4,4′‐tetraaminobiphenyl to prepare a polymer that was composed of repeating 2,5‐benzimidazole units. In contrast to previously prepared AB‐PBI, which contains only head‐to‐tail benzimidazole sequences, the new polymer also contains head‐to‐head and tail‐to‐tail benzimidazole sequences. The polymer was prepared in polyphosphoric acid (PPA) and cast into membranes using the sol–gel PPA process. Membranes formed from the new AB‐PBI were found to be mechanically stronger, possessed higher acid doping levels, and showed improved fuel cell performance, when compared to the previously known AB‐PBI. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012