摘要:
利用闪光光解(FP)将质谱学应用于气相光化学和动力学研究是从1957年开始的.由于能够用质谱法测定反应过程中各种不同的化学物种,探测反应物衰减和反应产物生长的动态速率,因此质谱法具有先进性和多用途.用于探测脉冲光解引起的反应物衰减和反应产物生长速率的质谱法,称为闪光光解时间分辨质谱法(FPTRMS).在进行实验时,使用闪光光解时间分辨质谱法能够从实验中获得直接的和有价值的反应动力学和反应机理信息.但是,有时也会受到条件限制,例如,一些实验研究只能在有限的温度和气压范围内进行,而另一些实验研究并不是都能够单独提供反应机理信息,特别是对于复杂体系.理论研究,包括原始计算法,RRKM(Rice-Ramsperger-Kassel Model)计算法和数字模拟计算法都只不过是实验研究有效的辅助手段.在较宽的温度和气压范围内,原始计算法和RRKM计算法都能用来预示化学反应速率系数,还能够从理论研究获得反应机理的重要信息.然而,理论研究获得的结果的合理性和准确性,最终还必须由实验结果予以证实和修正.作为一个实际例子,本工作叙述了使用闪光光解时间分辨质谱法和理论计算法研究CF3CHClO官能团的反应动力学及其反应机理.
关键词:
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质谱学
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理论计算
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闪光光解
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动力学
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机理
Abstract:
The application of mass spectrometry to investigations of gas-phase photochemistry and kinetics by flash photolysis was first reported in 1957. Mass spectrometry is advantageous and versatile for kinetics and mechanism studies since it is capable of detecting many different chemical species during the course of the reaction and one can determine kinetic rates of reactant decay and product growth. When the mass spectrometer is used to determine kinetic decays and growths following pulsed photolysis, it may be called flash photolysis with time-resolved mass spectrometry(FPTRMS). While experiments using FPTRMS can obtain direct and valuable information on kinetics and mechanism of chemical reactions, they are limited in some cases. For example, experiments can be conducted only at limited temperature and pressure ranges. Moreover, the experimental investigation alone does not always provide sufficient information for the reaction mechanism study, especially for a complex reaction system. The theoretical investigations including Ab Initio calculations, RRKM calculations and numerial simulations are useful and supplemental tools to the experimental studies. Ab initio and RRKM calculations can be used to predict rate coefficients of chemical reactions in a much wider ranges of temperature and pressure. Important information on the mechanism can also be obtained from the theoretical studies. However, the validation and accuracy of the results from the theoretical investigations need to be verified or adjusted by experimental results. As an example, a study of kinetics and mechanism of CF3CHClO radical reactions using FPTRMS combining with the theoretical calculations is reported.
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