Kinetic isotope effects (KIEs) in the free radical reactions-application to the atmospheric chemistry

大气痕量气体的稳定同位素分析对于提高我们对其来源、汇和输送的认识是非常有用的。其基本原理是，不同的来源具有特定的同位素比率，而且下沉过程伴随着同位素分馏。在过去的几年里，人们非常关注地球大气化学成分的变化，并对这个问题进行了大量的研究。最近研究的主要主题之一是甲烷。甲烷是一种重要的温室气体，其在平流层和对流层的相对浓度受到与OH、O(^1D)和Cl的反应的影响。环境中甲烷的源和汇的一个非常有用的指示器是通过测量^&lt；12&gt；C/^&lt；13&gt；C比率提供的，解释这些数据需要了解导致分馏的几个过程的动力学同位素效应(Kie)。动力学同位素效应(Kies)是同位素不同分子疼痛的速率常数的比率的大鼠。它们被广泛用作阐明反应机理的工具，并已在实验和理论上进行了研究。本课题利用高灵敏度的光电离质谱计建立了一种测定自由基反应KIes值的新方法。测定了甲基自由基(^&lt；12&gt；CH3，^&lt；12&gt；CH3，CD3)与原子或分子氧反应的Kie值。

Stable isotope analysis of atmospheric trace gases can be very useful in improving our understanding of their sources, sinks, and transport. The rationale is that various sources have characteristic isotopic ratios and that sink processes are accompanied by isotope fractionation. The last few years have witnessed great concern about changes in the chemical composition of the Earth's atmosphere, and a significant amount of research has been devoted to this questions. One of the principal subjects of the recent studies is methane. Methane is an important greenhouse gas whose relative concentrations in the stratosphere and troposphere is affected by reaction with the radicals OH, O (^1D), and Cl. A very useful indicator of the sources and sinks of methane in the environment is provided by measurements of the ^<12>C/^<13>C ratios, and interpretation of these data requires an understanding of the kinetic isotope effects (KIEs) of several processes that lead to fractionation. Kinetic isotope effects (KIEs) are rats of ratios of rate constants for pains of isotopically different molecules. They are widely used as tools for elucidating reaction mechanism and have been investigated both experimentally and theoretically. In this project a new method to determine the KIEs value of free radical reactions has been developed by using the high sensitive photoionization mass spectrometer. The KIEs values for reactions of methyl radicals (^<12>CH_3, ^<12>CH_3, CD_3) with atomic or molecular oxygen were determined.