The research seeks to establish the important high-pressure combustion chemistry need for practically important combustion processes, including internal combustion engines. Combustion efficiency and stability, internal engine knock, emission of environmentally noxious substances are the problems which require detailed chemical kinetics mechanisms with well-characterized elementary reactions over extended temperature and pressure ranges. However, the kinetic data necessary for advancement of combustion models at elevated pressures are still insufficient. Laboratory measurements usually provide rate constants at "convenient" pressures (0.001 - 1 bar). They are necessarily extrapolated to higher pressures based on theoretical foundations, but such predictions may introduce significant additional uncertainties into the model predictions. The specific research objective is a systematic fundamental study on the kinetics and mechanisms of unimolecular and bimolecular reactions of free radicals of combustion importance such as HCO, CH3, OH, and HO2 over extended temperature and elevated pressure ranges. Pulsed laser photolysis combined with high-pressure flow system and transient absorption-spectroscopy techniques will be used in the experimental studies. Buffer gas density affects the rates and branching ratios of dissociation and isomerization reaction, bimolecular reactions that proceed via an intermediate complex, as well as the corresponding reverse reactions. The comparison of the measurements of the pressure fall-off in this reaction with theoretical calculations will lead to the further advancement of the theory of unimolecular dissociation and the RRKM theory with isolated resonances. Overall, the proposed research program will contribute to extending the knowledge and understanding the buffer gas density effects. Broader impacts of the proposed work arise through publications and presentations in the technical and scientific community, by the education and training of students and new scientists, and through advancement of synergetic collaborations between disciplines and institutions, both domestic and international. The research will rely upon training and participation of graduate as well as undergraduate students.
