Theoretical Analysis of Atmospheric Reactions

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This project involves testing, extending, and applying high-accuracy theoretical methods to atmospheric chemical reactions. It consists of three tasks. Task 1 is to use theory to predict reaction rate constants and branching ratios for nitrogen-containing atmospheric species. Amines, imines, and amides are emitted from feedlots and other biogenic sources. Amines may contribute to future industrial emissions because they are key components of an industrial method for carbon dioxide capture (to reduce greenhouse gas emissions). Rate constants will be predicted for some reactions that have never been measured experimentally because the nitrogen-containing reactants are unstable. Task 2 is to further test the accuracy of Semi-Classical Transition Sate Theory (SCTST) by comparing predicted rate constants with experimental data for key atmospheric reactions. SCTST has already been shown to predict ab initio rate constants in excellent agreement with experiments for the reaction of hydroxyl radical with molecular hydrogen, without any empirical adjustments. It also predicts ab initio rate constants for chlorine atoms with methane in very good agreement with experiments. The predicted hydrogen/deuterium kinetic isotope effects (KIEs) for both reactions are as accurate as the existing experimental data. SCTST will be characterized further and then used to predict rate constant and KIEs for several additional atmospheric reactions. Task 3 is to extend the Master Equation treatment of unimolecular and recombination reactions by explicitly incorporating conservation of angular momentum. This will significantly improve on existing Master Equations, which use various untested approximations to avoid the explicit treatment. The new Master Equation will be used to generate benchmarks and can be used to predict rate constants and to analyze experimental data.All areas of gas phase chemical kinetics will benefit from the characterization of SCTST. The benchmark Master Equation calculations will enable other researchers to test models for non-equilibrium chemical systems where collisions and chemical reactions are competitive. These include combustion, chemical manufacturing, planetary atmospheres, and astrochemistry. The results, parameterizations, source codes, and all models will be presented at scientific meetings, published in the peer-reviewed literature, and made freely available on the internet. These materials will add to the cyberinfrastructure of atmospheric chemistry. Students and postdoctoral research associates will be trained in the development and use of computational chemical kinetics methods.