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) x 10(16) 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: k(1)(infinity) = 2.36 x 10(-11) exp(433 KIT), k(2)(infinity) = 3.06 x 10(-11) exp(387 KIT), and k(3)(infinity) = 2.28 x 10(-11) exp(473 K/T) cm(3) molecule(-1) s(-1). C3H8 was detected as a product of reaction 1 and C5H12 and C4H8 were detected as products of reaction 3.