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221.
《Theoretical chemistry accounts》1997,95(5-6):201-213
Summary. Thermal one- and two-bond dissociation processes of cis- and trans-azomethane were studied by ab initio computation with DZP and TZ2P basis sets, using the d(N–C) bond lengths as the reaction coordinates. The geometries were optimized at the MP2 level, and the dissociation energies
obtained exploiting a single-point, fourth-order M?ller–Plesset calculations [MP4SDTQ/TZ2P]. At this level of theory including
zero-point energies, the trans-isomer is by 9.3 kcal/mol more stable than the cis-isomer. The results show that the energetically more favourable one-bond cleavage proceeds without transition state with
the predicted bond dissociation energy D
0 of 47.8 kcal/mol for trans-azomethane and 38.5 kcal/mol for cis-azomethane. With calculated barrier heights the unimolecular dissociation rate constants have been determined by means of
the RRKM theory. The second-order saddle points localized for synchronous decomposition pathways lie 13 (trans)-23(cis) kcal/mol above the one-bond dissociation energies [MP2/DZP].
Received May 28, 1996/Final version received November 1, 1996 / Accepted November 1, 1996 相似文献
222.
B A Finnin M A A O'Neill S Gaisford A E Beezer J Hadgraft P Sears 《Journal of Thermal Analysis and Calorimetry》2006,83(2):331-334
Isothermal
calorimetry is becoming indispensable as a tool for the study of a wide variety
of systems. As with all scientific instruments it is essential that robust
calibration routines be developed in order to validate the data obtained.
Chemical test reactions offer many advantages over (the traditionally used)
joule effect heating methods, not least because they have the potential to
validate instrument performance (i.e. they can be used to assess all aspects
of calorimeter operation). In this work the results of a validation exercise,
conducted by Thermal Hazard Technology as part of an installation routine,
using the base catalysed hydrolysis of methyl paraben are discussed. In the
case described, a systematic misreporting of the reported temperature of a
calorimeter was identified, caused by an upgrade to the calorimeter's
firmware, a discrepancy which may not have been noted using traditional electrical
calibration methods and one which highlights the importance of both manufacturers
and end-users adopting chemical test reactions into their test and validation
routines. 相似文献
223.
224.
Thermogalvanic cells(also known as thermo-electrochemical cells) that convert waste heat energy to electricity are a new type of energy conversion device. However, the electron transfer kinetics and mass transfer of redox couples have not been thoroughly studied. Here, the ion reaction and charge transport in thermogalvanic cells are investigated by electrochemical impedance analysis. We first propose the detailed impedance model followed experimental verification on three types of electrode materials. Parameters including kinetic rate constants and ion diffusion coefficients for the electrodes are obtained by fitting the impedance data. Our study shows explicitly that impedance analysis can provide useful information on selecting suitable electrode materials for thermogalvanic cells. 相似文献
225.
John E. Nicholas Andrew I. Spiers Nicholas A. Martin 《Plasma Chemistry and Plasma Processing》1986,6(1):39-51
Studies of time-resolved absorption spectra of transient species in the decomposition of NH3 by an r.f. pulse discharge together with product analysis showed that the major radical formed was NH at concentrations of the order of 10–6 mol dm–3 (105 molec. cm–3). Possible mechanisms for the formation of the radical during the discharge and its decay following pulse cut-off were tested by computer simulation of the kinetic data. Following zero-order formation with rate coefficient 0.19±0.03 mol dm–3 s–1, the decay was second order in NH with rate coefficient 2.1±0.5×109 mol–1 dm3 s–1 both for pure NH3 and where NH3/rare gas mixtures were investigated. The kinetic data are consistent with NH removal in a nonassociative radical-radical reaction proceeding via a short-lived collision complex, probably 2NH N2H2 N2 + H2. 相似文献
226.
The kinetic curves at infinite temperature for the solid-state reactions of the interface shrinkage type were drawn theoretically by taking account the particle size distribution in the sample mixture. The CRTA curves for the reactions with the particle size distribution can be drawn by utilizing the universal kinetic curves at infinite temperature. The proper kinetic treatment for the CRTA curves with the particle size distribution is discussed in connection with the property of the kinetic equation with respect to the particle size distribution. The present kinetic consideration is taken as a simulation for the reactions with a certain distribution in among the reactant particles, produced preferably by the mass and heat transfer phenomena during the thermoanalytical measurements. The merit of the rate jump method by a single cyclic CRTA curve is also discussed on the basis of the present results. 相似文献
227.
S. O. Bondareva V. V. Lisitskii N. I. Yakovtseva Yu. I. Murinov 《Russian Chemical Bulletin》2004,53(4):803-807
The kinetics of hydrolysis of 1,2-disubstituted imidazolines in aqueous media was studied (pH 2.0—12.5, T = 25—90 °C) by UV spectroscopy. The hydrolysis products were identified. The introduction of a branched substituent into position 2 of the imidazoline ring increases the hydrolytic stability of the compounds. The effect of the pH on the hydrolysis rate of imidazolines is discussed. 相似文献
228.
单向应力条件下松弛时间率相关的非线性粘弹性本构模型 总被引:1,自引:0,他引:1
基于单向拉伸实验研究和内变量理论 ,提出了一种新的简单的一维非线性粘弹性本构关系 .对两种粘弹性材料 ,即高密度聚乙烯和聚丙烯进行了不同加载速率作用下的拉伸实验研究 ,实验结果表明 ,两种材料的应力应变关系与加载速率相关 ;对材料的应力应变实验数据进行拟合发现 ,材料的松弛时间具有很强的应变率相关性 ,当应变率发生数量级变化时 ,材料的松弛时间也发生数量级的变化 .采用内变量理论 ,导出了在单轴应力条件下松弛时间率相关的非线性粘弹性本构关系的迭代形式 ,并给出其收敛条件 .当采取一次迭代形式时 ,本构关系退化为松弛时间率相关的Maxwell模型 .数值拟合的结果表明 ,一次迭代形式的本构关系就可以很好地拟合和预测实验结果 . 相似文献
229.
230.
《Surface and interface analysis : SIA》2003,35(5):445-449
Surface states of polydimethylsiloxane (PDMS) treated by plasma were investigated by x‐ray photoelectron spectroscopy and surface voltage decay. X‐ray photoelectron spectroscopy confirmed the formation of a silica‐like (SiOx, x = 3–4) oxidative surface layer. This layer increased in thickness with increasing exposure duration of plasma. Plasma exposure lowers the surface resistivity from 1.78 × 1014 to 1.09 × 1013 Ω □?1 with increasing plasma treatment time. By measuring the decay time constant of surface voltage, the calculated surface resistivity was compared with the value measured directly by a voltage–current method; good agreement between the two methods was obtained. It was observed that plasma treatment led to a decrease in the thermal activation energy of the surface conduction from 31.0 kJ mol?1 for an untreated specimen to 21.8 kJ mol?1 for a plasma‐treated specimen for 1 h. Our results allow the examination of effects of plasma on the electrical properties of PDMS. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献