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Abstract
Isomer-resolved speciation experiments were conducted to probe the temperature and oxygen dependence of intermediates from the unimolecular decomposition and secondary-O2 addition to hydroperoxybutyl radicals. These intermediates serve as modeling targets to constrain and improve chemical kinetics mechanisms necessary for modeling combustion. The experiments were conducted in a jet-stirred reactor (JSR) using an initial concentration of 2% n-butane at 810 torr from 500 – 900 K. Oxygen concentrations were varied at two temperatures, 650 K and 800 K, which were the two temperatures where intermediate formation reached a maximum. Steady-state intermediate production was quantified using vacuum-ultraviolet spectroscopy and electron-impact mass spectrometry. All constitutional and stereoisomers of cyclic ethers were separated and quantified for the first time. Two carbonyl species, methyl vinyl ketone and diacetyl, were quantified the first time and are important to understanding chain-branching reactions. The oxygen dependence of these carbonyls displayed the same trends as chain-propagating intermediates instead of chain-branching intermediates, indicating a notable discrepancy between measured and model-predicted species profiles.