Effect of the enthalpy,sample size and heating rate on the cure reaction of rubber in dsc

As a continuation of the recent studies devoted to the determination of profiles of temperature and state of cure developed through the sample when heated in a calorimeter working in scanning mode, the effect of the enthalpy of reaction, of rather low value, on these profiles was investigated. The effect of the cure enthalpy on the heat flux emitted through the sample-calorimeter interface was especially studied, for various heating rates and various sample sizes. Moreover, the effect of a change of this cure enthalpy on the heat flux and profiles of temperatures and state of cure was determined and reported. These results were obtained not only by experiments in case of the size of the sample available for our calorimeter, but also by calculation with the help of a numerical method with finite differences. This model took into account heat transferred by conduction and the heat generated by the cure reaction.     

Quantum Wave Packet Studies on F ＋ HBr Reaction

IntroductionA series of reactions of fluorine atoms with hydro-gen halidesF HCl HF Cl (1)(ΔH—00=-137·10 kJ/mol)F HBr HF Br (2)(ΔH—00=-202·73 kJ/mol)F HI HF I (3)(ΔH—00= -270·45 kJ/mol)belongs to the prototypical heavy-light-heavy reactionsa     

S1 ← S0 laser excitation spectra of glyoxal in a supersonic jet: High-resolution rotational analysis

The high-resolution rotational spectra of several S₁ ← S₀ vibrational transitions of glyoxal are obtained and analyzed. Undispersed fluorescence excitation spectra are obtained with a CW ring dye laser in a supersonic jet, providing a linewidth down to 100 MHz. Rotational constants and band origins are determined with an asymmetric rotator program. Population distribution in the supersonic jet is studied. The overtones of the torsion mode (ν₇) are examined as an approach to the trans-cis potential barrier. The 8₀¹ and 8₀¹ 7₀² bands of A + B type, which are too congested at room temperature experiments, are well resolved in this jet experiment. As a result, the rotational constants obtained by fitting low-J and -K rotational transitions are in good agreement with the constants obtained by fitting large-J and -K transitions of room temperature spectra. Furthermore, on about 1000 analyzed lines no rotational perturbation has been observed.     

Time-dependent mass spectra and breakdown graphs. 10. Dissociative photoionization of anisole

Time-resolved photoionization mass spectrometry in the millisecond range has been employed to study the reaction C₆H₅OCH⁺₃ → C₆H⁺₆ + CH₂O in anisole. Photoionization efficiency (PIE) curves gave a long-time limiting appearance energy value, AE = 10.85 ± 0.05 eV at 298 K. Experimental PIE curves and breakdown graphs at t = 6 μs and 2 ms were compared to those predicted by the statistical theory (RRKM/QET) and by previous photoelectron—photoion coincidence spectrometry results. A sensitivity analysis yielded the following activation parameters: critical energy of activation, E₀ = 59.6 ± 0.6 kcal/mol, and entropy of activation, ΔS³(1000 K) = 7.25 ± 2.2 eu.     

Quasiclassical trajectory study of the reaction O(3P) + HI → OH + I

Three-dimensional quasiclassical trajectory calculations were carried out for the reaction of oxygen atoms O(³P) with hydrogen iodide molecules (HI and DI) for the temperature range 200–550 K, using a LEPS potential-energy surface. The calculated results include reaction cross sections, rate constants, kinetic isotope effects, the influence of vibrational and rotational excitation of the reactants on the dynamics, and the product energy partitioning and angular distribution. The calculated results are in good agreement with the available experimental results. The dynamics of the O + HI reaction is discussed in view of the associated mass combination H + LH′ (H and H′ are heavy atoms and L is a light atom), and in relation to earlier trajectory results for the reactions O + HCl and O + HBr.     

Dissociative nitrogen chemisorption and bonding on Gd(0001)

The electronic structure of dissociatively chemisorbed nitrogen on Gd(0001) has been studied using angle-resolved photoemission at 150 K. The symmetry of the nitrogen-induced states and bonding configuration for the initial chemisorption has been identified. Bonding occurs above the Gd(0001) surface plane via the N p_z orbital. Two possible adsorption sites are postulated, with preferential occupancy that is dependent upon coverage.     

16通道毛细管阵列电泳对手性氨基酸分离条件的快速筛选

利用自行研制的16通道旋转激光扫描共焦荧光检测式毛细管阵列电泳仪,我们采用了不同浓度的十二烷基硫酸钠、β-环糊精、γ-环糊精对荧光素标记丙氨酸、甲硫氨酸、色氨酸和谷氨酸4种手性氨基酸进行了手性拆分条件研究,快速地获得了这4种手性氨基酸对映体最佳的拆分条件:分离缓冲液为10 mmol/L硼酸缓冲液(pH=10),5 mmol/Lγ-环糊精为添加剂时,4种手性氨基酸全部达到了基线分离。     

Chemisorption and dissociation of O2, on Ag(110)

Using an Ag₂₄ cluster, we have calculated the potential energy surface of an O₂ molecule chemisorbing and dissociating on the Ag(110) surface, with its molecular axis parallel to the grooves in the [1̄10] direction. For molecular chemisorption, we find equilibrium positions and vibrational frequencies in good agreement with experiment and with earlier calculations; the chemisorption energy, ∼ 0.1 eV, may be somewhat too low. Although both our calculated and the experimental vibrational frequencies suggest a chemisorbed O²⁻₂ ion, our calculated charge transfer to the O₂ molecule is a little less than one electron. We can explain the calculated low OO strength frequency by changing occupations of OO bonding and antibonding states with changing OO separation. These results show that one has to be cautious in directly relating observed vibrational frequency lowerings of chemisorbed molecules to their charge states. The dissociation path is completely along the direction of the OO stretch; we find a barrier height of ∼ 0.2 eV. The atomic equilibrium distance, vibrational frequency, and binding energy are in reasonable agreement with experiment. At large OO separation, the energy still decreases with increasing OO distance, indicative of OO Coulomb repulsion.