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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Time-resolved cavity ringdown measurements and kinetic modeling of the pressure dependences of the recombination reactions of SiH2 with the alkenes C2H4, C3H6, and t-C4H8
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Time-resolved cavity ringdown measurements and kinetic modeling of the pressure dependences of the recombination reactions of SiH2 with the alkenes C2H4, C3H6, and t-C4H8

机译：SiH2与烯烃C2H4，C3H6和t-C4H8重组反应的时间分辨腔衰荡测量和动力学模型的压力依赖性

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摘要

Room-temperature rate constants for the pressure-dependent reactions SiH2 + ethene, propene, and t-butene have been determined at total pressures of 3.3 mbar <= p <= 300 mbar with Ar as buffer gas. SiH2 was detected by means of time-resolved cavity ringdown spectroscopy (CRDS), and the deconvolution of ringdown, kinetics, and laser bandwidth effect was accomplished with the extended simultaneous kinetics and ringdown model (eSKaR). In this way, pseudofirst-order rate constants could be extracted from nonexponential ringdown profiles. The recombination reactions, including the reaction SiH2 + i-butene, have been modeled based on the simplified statistical adiabatic channel model (SACM) and weak collision energy-grained master equation (ME) simulations. The influence of an interfering fast isomerization channel was investigated based on the Rice, Ramsperger, Kassel, Marcus theory (RRKM) and was found to be only important for the C2H4 reaction. Using ab initio energies (G3) and structures (MP2/6-311G(d,p)) as input parameters for the kinetic models, a consistent description of the pressure and temperature dependences of all four reactions was possible. In the temperature range 295 K <= T <= 600 K, the extrapolated limiting high-pressure rate constants, k(infinity)(C2H4)/(cm(3)center dot mol(-1)center dot s(-1)) = 1.9 x 10(14) (T/K)(-0.065), k(infinity)(C3H6)/(cm(3)center dot mol(-1)center dot s(-1)) = 1.3 x 10(14) (T/K)(0.075), k(infinity)(i-C4H8) = 1.8 x 10(14) cm(3)center dot Mol(-1)center dot s(-1), and k(infinity)(t-C4H8)/(cm(3)center dot mol(-1)center dot s(-1)) = 4.6 x 10(13) (T/K)(0.21), are close to the collision number and are more or less temperature independent. In the case of ethene, probably due to the approximate treatment of rotational effects and/or the interfering isomerization process, the applied model slightly underestimates the falloff and thus yields too high extrapolated rate constants at p < 10 mbar.
机译：压力依赖性反应SiH2 +乙烯，丙烯和叔丁烯的室温速率常数已经确定，总压力为3.3 mbar <= p <= 300 mbar，Ar作为缓冲气体。通过时间分辨腔衰荡光谱（CRDS）检测SiH2，并通过扩展的同时动力学和衰荡模型（eSKaR）实现衰荡，动力学和激光带宽效应的解卷积。以此方式，可以从非指数振铃曲线提取伪一阶速率常数。基于简化的统计绝热通道模型（SACM）和弱碰撞能量粒度主方程（ME）模拟，对包括反应SiH2 +异丁烯在内的重组反应进行了建模。基于莱斯，拉姆斯伯格，卡塞尔，马库斯理论（RRKM），研究了干扰快速异构化通道的影响，发现该干扰仅对C2H4反应重要。使用从头算能量（G3）和结构（MP2 / 6-311G（d，p））作为动力学模型的输入参数，可以对所有四个反应的压力和温度依赖性进行一致的描述。在295 K <= T <= 600 K的温度范围内，外推极限高压率常数k（无穷大）（C2H4）/（cm（3）中心点mol（-1）中心点s（-1） ）= 1.9 x 10（14）（T / K）（-0.065），k（无穷大）（C3H6）/（cm（3）中心点mol（-1）中心点s（-1））= 1.3 x 10 （14）（T / K）（0.075），k（无穷大）（i-C4H8）= 1.8 x 10（14）cm（3）中心点Mol（-1）中心点s（-1）和k（无限）（t-C4H8）/（cm（3）中心点mol（-1）中心点s（-1））= 4.6 x 10（13）（T / K）（0.21），接近碰撞数并且或多或少与温度无关。在乙烯的情况下，可能是由于旋转效应和/或干扰异构化过程的近似处理，所应用的模型略微低估了衰减，因此在p <10 mbar时会产生过高的外推速率常数。

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