A novel apparatus for pulsed laser photolysis generation of radicals coupled with laser induced fluorescence (LIF) detection of OH has been developed at the University of York, enabling kinetic studies of atmospheric and combustion-relevant chemical reactions.
Direct LIF detection was used to identify unambiguously OH as a product of O2 + RCO reactions, for the first time, where R = CH3CH2CH2, (CH3)2CH, (CH3)3C, CH3CH2CH2CH2, (CH3)2CHCH2, and CH3CH2CH(CH3). Pressure- dependent (13 - 120 Torr) OH yields were determined by comparison of time-resolved OH LIF profiles with those obtained from the well-characterised CH3CO + O2 → OH reaction. Results not only illustrate the dependency of OH yield on chain length and degree of branching within the R group, but also resolve a literature discrepancy for CH3CH2CO + O2 .
OH produced from RCO + O2 was used as a spectroscopic marker to study the kinetics of Cl + RCHO. This indirect method produced the first values for Cl + (CH3)2CHCH2CHO ((3.1 ± 0.6) × 10−10 cm3 molecule−1 s−1) and CH3CH2CH(CH3)CHO ((1.2 ± 0.3) × 10−10 cm3 molecule−1 s −1) at 298 K, with results for other Cl + RCHO and OH + RCHO reactions agreeing well with previous literature.
Finally, the reactions of RC(O)O2 with HO2 were investigated at temperatures between 293 and 400 K. Preliminary experiments in the absence of HO2 recorded OH production from a previously unknown source, potentially RC(O)O2 + RC(O)O2. OH production from RC(O)O2 + HO2, identified for the first time when R = CH3CH2, (CH3)2CH, (CH3)3C, (CH3)2CHCH2, and CH3CH2CH(CH3), demonstrates that significant OH production is a general feature of HO2 + RC(O)O2 reactions.
