Kinetics of the Reactions of n-Alkyl (C2H5, n-C3H7, and n-C4H9) Radicals with CH3

The ethyl-methyl, n-propyl-methyl, and n-butyl-methyl cross-radical reactions were studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 297−800 K and bath gas (helium) density (3−36) × 1016 atom cm-3. The observed overall C2H5 + CH3 (1), n-C3H7 + CH3 (2), and n-C4H9 + CH3 (3) rate constants demonstrate negative temperature dependences. Master equation modeling of collisional effects indicates that the n-C3H7 + CH3 and the n-C4H9 + CH3 reactions are at the high-pressure limit under all experimental conditions used. The C2H5 + CH3 reaction is not at the high-pressure limit and falloff in reaction 1 cannot be neglected at 800 K. Falloff corrections applied to reaction 1, on average, reach 45% at 800 K and introduce noticeable uncertainties in the extrapolated high-pressure-limit rate constant values. The following expressions for the high-pressure-limit rate constants of reaction 1−3 were obtained:  k1∞ =...