气相亚硝酸烷基二酯电子轰击电离解离机理研究

摘要

亚硝酸烷基二酯(R2C(ONO)(CH2)nC(ONO)R2)因其双官能团的特殊性而具有极高活性,在大气中极易产生烷氧自由基和氮氧化物,从而导致温室效应和光化学污染.因此研究亚硝酸烷基二酯的解离机理对理解其在大气中的光化学及热化学过程具有重要意义.本文采用气质联用(GC-MS)等方法研究了6种二酯(1,2-、1,3-亚硝酸丙二酯,1,2-、2,3-和1,4-亚硝酸丁二酯和1,5-亚硝酸戊二酯)在70 eV电子轰击下的解离过程,发现断裂碎片对二酯的结构具有特征性指示作用.我们发现除常见O-NO键断裂产生的NO+碎片离子峰外,同时也观测到因αC-C键断裂产生的R2C(ONO)+碎片离子峰.通过对不同产物碎片所对应的解离路径的分析得出亚硝酸烷基二酯不同于其热解及光解的解离机理,即其直接发生O-NO键或C-C键的断裂.%Alkyl dinitrites with two functional groups,R2C(ONO)(CH2)nC(ONO)R2,can easily produce alkoxy radicals and nitric oxide in the atmosphere.Their high activity has led to issues such as photochemical air pollution and the greenhouse effect.Hence,unraveling the decomposition mechanism of alkyl dinitdtes is of great significance in understanding their photochemical and thermochemical roles in the atmosphere.In this work,the dissociation process of six alkyl dinitrites was investigated by mass spectrometry under the electron impact energy of 70 eV.Our results indicated that the ruptured fragments had characteristic directivity for the structures of alkyl dinitrites.We detected not only the NO+ fragment ion,due to the common breakage of O-NO bond,but also R2C(ONO)+ resulting from the breakage of α C-C bond in the electron ionization mass spectra.The dissociation mechanism of alkyl dinitrites in which the O-NO or C-C bond directly dissociates is different from photolysis and pyrolysis.