阿尔法蒎烯臭氧分解反应的极紫外自山电子激光光电离质谱研究

Vacuum Ultraviolet Free-Electron Laser Photoionization Mass Spectrometry of Alpha-pinene Ozonolysis

阿尔法蒎烯是大气中含量最高的自然源萜类挥发性有机物,其臭氧化分解反应会产生大量的反应中间体和产物,精确表征这些物种被认为是大气化学最前沿、最具挑战性的课题之一.本文利用极紫外自由电子激光光电离质谱方法,研究了阿尔法蒎烯的臭氧分解反应机理.该反应是在2立方米的烟雾箱中进行,利用气动透镜把产生的气溶胶传输到质谱探测腔室,利用极紫外自山电子激光对气溶胶进行单光子软电离,测得了常规实验方法难以得到的飞行时间质谱,发现了一系列新物种.与量子化学理论计算相结合,揭示了这些新物种的反应机理.这些研究结果从分子水平上揭示了蒎烯的臭氧分解反应机制,有助于理解大气雾霾微观机理.

α-pinene is the most abundant monoterpene that represents an important family of volatile organic compounds.Molecular identification of key transient compounds during theα-pinene ozonolysis has been proven to be a challenging experimental target because of a large number of intermediates and products involved.Here we exploit the recently developed hybrid instruments that integrate aerosol mass spectrometry with a vacuum ultraviolet free-electron laser to study theα-pinene ozonolysis.The experiments ofα-pinene ozonolysis are performed in an indoor smog chamber,with reactor having a volume of 2 m^(3) which is made of fluorinated ethylene propylene film.Distinct mass spectral peaks provide direct experimental signatures of previously unseen compounds produced from the reaction ofα-pinene with O_(3).With the aid of quantum chemical calculations,plausible mechanisms for the formation of these new compounds are proposed.These findings provide crucial information on fundamental understanding of the initial steps ofα-pinene oxidation and the subsequent processes of new particle formation.