Experimental and computational studies of elementary reactions involving small radicals

1. 0 O(3P) + C2F4(1Ag) F2(2P) + F3CCO(X2A`) -20 F2(2P) + F2CCFO(X2A») (T) -40 ISC (S) CF3(X2A1) + CFO(2A’) -60 Relative energy (kcal/mol) Rapid relaxation -80 CF2 + F2CO -100 -120 (Cs,X1A’) (C2v,X1A1) -140 CF4 + CO Experimental and computational studies of elementary reactions involving small radicals The kinetics group carries out research to characterise, predict and understand the nature of elementary photochemical and chemical reactions (see the bottom picture). We focus on improving the understanding of the chemical reactivity of small radicals in general and on providing rate constants and product distributions of elementary reactions that can be used in complex chemical kinetic models of systems, such as the atmosphere of Earth, other planetary atmospheres, combustion process, and plasmas. Reactions are studied experimentally using advanced laser-spectroscopic techniques and quantum statistically using sophisticated and powerful computer code. The following projects, subdivided into areas of application, are available in the group. The accompanying poster gives additional information for each project. Atmospheric chemistry AReactivity of electronically-excited oxygen atoms The electronically-excited atom, O(1D), is generated in the Earth’s atmosphere by photo-dissociation of ozone. It’s subsequent reaction with gas-phase H2O is the dominant source of the most important reactive species in the atmosphere, OH. In this project, rate constants for reactions of O(1D) with other important atmospheric molecules will be determined using a pulsed laser photolysis \ time-resolved chemiluminescence technique, recently developed in this group with particular focus on the ratio of chemical reaction rate to electronic quenching. B Degradation pathways of organic molecules Degradation of organic material in the atmosphere is usually started by a reaction with OH- or NO3 radicals, or ozone, followed by a (branching) sequence of reactions with O2, NO, ROO radicals and/or isomerisations. Biogenic sesquiterpenes, C15H24 compounds, are an important class of hydrocarbons; we wish to study their O3-initiated oxidation. The project will involve the use and interpretation of high-level quantum mechanical and quantum statistical calculations Combustion chemistry CReactivity of the ketenyl radical, HCCO Combustion of fossil fuels will remain an important source of energy for many years. There is therefore great impetus to reduce pollutant emissions (e.g., CO2, NO, soot) from these processes. An effective strategy for the reduction of NOx emissions is, so-called “reburning”. For this reduction technique, combustion parameters are modified such that a region is created having high fuel-to-air ratio and relatively low temperature. Chemical kinetic modelling reveals that, under these conditions, removal of NO is achieved by a series of reactions beginning with, amongst others, HCCO + NO and ultimately producing N2. The aim of this project is to further characterise the reactivity of HCCO in combustion environments (for which relatively little data exists) using advanced time-resolved, high-resolution laser spectroscopic techniques. Planetary and interstellar chemistry DReactivity of the C2H radical in Titan’s atmosphere The temperature of Titan’s atmosphere ranges from ca. 70 K to ca. 170 K. In this cold environment, chemistry is usually dominated by reactions having no energy barrier, such as often occurs between two radicals. We have recently shown, however, that the C2H radical, present in Titan’s atmosphere, unusually undergoes barrier-less reactions with several molecules (SO2, H2S, HCHO, NH3) such that it is expected to play a significant role in the complex atmospheric chemistry. A project is available that will further study the reactivity of C2H focusing primarily on determination of rate constants as a function of temperature and pressure, for reaction of C2H with certain cyanoalkenes or cyanoalkynes. Titan ca. 95% N2 4% CH4 Part of the energetic pathway traversed by an elementary chemical reaction Reaction chamber intersected by three pulsed laser beams for detection of HCCO Contact Prof. S. Carl Rm: 03.07