An Experimental and Computational Investigation of the Kinetics of Branched Butyl Radicals 2-Methylpropan-1-yl and 2-Methylpropan-2-yl with Molecular Oxygen.

We have measured the rate coefficient for the reaction between the 2-methylpropan-1-yl radical and molecular oxygen as a function of temperature and pressure in both He and N2 bath gases using photoionization mass spectrometry. Similar measurements were performed for the 2-methylpropan-2-yl radical. It was found that 2-methylpropan-1-yl reacts much slower with O2 than 2-methylpropan-2-yl both in the falloff region and near the high-pressure limit. We complemented the experimental work by constructing master-equation models for both reaction systems to simulate their kinetics under conditions not covered by experiments. By optimizing the value of few key parameters against measured data, the models were able to reproduce the observed temperature and pressure dependencies of both rate coefficients. To facilitate the use of present results in modeling, PLOG and Chebyshev rate-coefficient parametrizations are provided. Although 2-methylpropan-1-yl reacts much slower with O2 than 2-methylpropan-2-yl, the former reaction generates more products that lead to chain-propagation and -branching than the latter, which almost exclusively forms 2-methylpropene and hydroperoxyl and is thus chain-terminating.