SynchroKin

Gas-phase chemical reactions are important in a wide variety of environments such as combustion, Earth’s atmosphere, and dense interstellar clouds. Modeling such environments requires a detailed understanding of the mechanisms and rate coefficients of key reactions that define the system. In combustion systems, the fuel oxidation mechanism influences the efficiency of the process and the formation of pollutants, and so is intimately linked to the chemistry of the atmosphere. In the atmosphere, the oxidation mechanism of volatile organic compounds (VOC) influences regional air quality and hence human health. On a global scale it affects the oxidizing capacity of the atmosphere and with this the global climate: on the one hand through effects on the lifetime of greenhouse gases such as methane, and on the other hand via tropospheric ozone chemistry and formation of secondary organic aerosols (SOA). A good knowledge of gas phase chemistry is required for a good description of dense interstellar clouds evolution. In general, these gas-phase chemical systems are driven by reactions of short-lived intermediates: radicals such as OH or HO2. A classical way of investigating these reactions is to produce these radicals in the presence of reactants, and to subsequently monitor the removal of the radicals and/or the formation of reaction products in a time resolved manner. Despite the progress that has been made over the last decades in gas-phase chemical kinetics, many key systems are still far from being understood. As the complexity of the reaction process increases, simultaneous detection of intermediate and final reaction products becomes a powerful tool for unravelling details of reaction. Mass spectroscopy (MS) is the technique of choice for such experiments, because, in principle, all species can be detected after ionization. However, the information available from MS depends critically on the ionization source: the most commonly employed methods may produce excessive fragmentation, making the mass spectra difficult to interpret, or lack the resolution to separate possible isomers. Here we propose to employ synchrotron radiation as the ionization source for a Time of Flight Mass Spectrometer (TOFMS). This apparatus will combine the multiplexing capabilities of a TOFMS with the high resolution and widely tunable VUV light of a synchrotron. We will couple this detector to a versatile chemical kinetic reactor, suitable for generating various radicals by two different and complementary methods: pulsed laser photolysis or continuous microwave discharge. The reactor will be temperature-controlled in order to access relevant temperatures from atmospheric to combustion conditions. The machine will be able to produce three dimensional maps of a reaction as a function of reaction progress, mass, and ionization energy, thus providing a truly universal detection system. The first such system, based on laser photolysis, was designed by our partner from Sandia using the VUV light of the Advanced Light Source (ALS) in Berkeley, CA. However, the incorporation of electron/ion coincidence techniques in the TOFMS, enabling unprecedented resolution of isomeric species and energy states, and the highly versatile chemical reactor will make the proposed apparatus a uniquely powerful and world-leading kinetics facility. The goal of this state-of-the-art instrument is to study important gas-phase reactions in unprecedented detail over a large range of temperature and pressure. At the end of this project the machine will be available to the national and international community and will continue over many years to improve our understanding of fundamental processes in atmospheric and combustion chemistry as well as astrochemistry.