Taatjes Craig A, Hansen Nils, Osborn David L, Kohse-Höinghaus Katharina, Cool Terrill A, Westmoreland Phillip R
Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, CA 94551-0969, USA.
Phys Chem Chem Phys. 2008 Jan 7;10(1):20-34. doi: 10.1039/b713460f. Epub 2007 Nov 6.
The combination of multiplexed mass spectrometry with photoionization by tunable-synchrotron radiation has proved to be a powerful tool to investigate elementary reaction kinetics and the chemistry of low-pressure flames. In both of these applications, multiple-mass detection and the ease of tunability of synchrotron radiation make it possible to acquire full sets of data as a function of mass, photon energy, and of the physical dimension of the system, e.g. distance from the burner or time after reaction initiation. The data are in essence an indirect image of the chemistry. The data can be quantitatively correlated and integrated along any of several dimensions to compare to traditional measurements such as time or distance profiles of individual chemical species, but it can also be directly interpreted in image form. This perspective offers an overview of flame chemistry and chemical kinetics measurements that combine tunable photoionization with multiple-mass detection, emphasizing the overall insight that can be gained from multidimensional data on these systems. The low-pressure flame apparatus is capable of providing isomer-resolved mass spectra of stable and radical species as a function of position in the flame. The overall chemical structure of the flames can be readily seen from images of the evolving mass spectrum as distance from the burner increases, with isomer-specific information given in images of the photoionization efficiency. Several flames are compared in this manner, with a focus on identification of global differences in fuel-decomposition and soot-formation pathways. Differences in the chemistry of flames of isomeric fuels can be discerned. The application of multiplexed synchrotron photoionization to elementary reaction kinetics permits identification of time-resolved isomeric composition in reacting systems. The power of this technique is illustrated by the separation of direct and dissociative ionization signals in the reaction of C(2)H(5) with O(2); by the resolution of isomeric products in reactions of the ethynyl (C(2)H) radical; and by preliminary observation of branching to methyl + propargyl products in the self-reaction of vinyl radicals. Finally, prospects for future research using multiplexed photoionization mass spectrometry are explored.
将多路复用质谱与可调谐同步辐射光电离相结合，已被证明是研究基元反应动力学和低压火焰化学的有力工具。在这两种应用中，多质量检测以及同步辐射易于调谐的特性使得获取作为质量、光子能量以及系统物理尺寸（例如距燃烧器的距离或反应开始后的时间）函数的全套数据成为可能。这些数据本质上是化学过程的间接图像。这些数据可以沿着几个维度中的任何一个进行定量关联和整合，以便与传统测量（如单个化学物种的时间或距离分布）进行比较，但也可以直接以图像形式进行解释。本视角概述了将可调谐光电离与多质量检测相结合的火焰化学和化学动力学测量，强调了从这些系统的多维数据中可以获得的整体见解。低压火焰装置能够提供稳定和自由基物种的异构体分辨质谱，作为火焰中位置的函数。随着距燃烧器距离的增加，从不断演变的质谱图像中可以很容易地看到火焰的整体化学结构，光电离效率图像中给出了异构体特异性信息。以这种方式比较了几种火焰，重点是识别燃料分解和烟灰形成途径中的整体差异。可以辨别异构燃料火焰化学的差异。将多路复用同步辐射光电离应用于基元反应动力学，可以识别反应系统中时间分辨的异构体组成。该技术的强大之处体现在以下方面：在C(2)H(5)与O(2)反应中分离直接电离和解离电离信号；在乙炔基（C(2)H）自由基反应中分辨异构体产物；以及在乙烯基自由基自反应中初步观察到生成甲基 + 炔丙基产物的分支情况。最后，探讨了使用多路复用光电离质谱进行未来研究的前景。
