Rate constants for the reactions of CH3 radicals with C2H5, i-C3H7 and t-C4H9 radicals

Abstract

Molecular modulation spectrometry has been used to measure the overall cross-reaction rate constants for the reactions of CH3 radicals with C2H5, i-C3H7 and t-C4H9 radicals at 308 K. The values of the rate constants obtained are (in cm3 mol–1 s–1): CH3+ C2H5, k=(28.5 ± 2.2)× 1012; CH3+ i-C3H7, k=(24.3 ± 2.3)× 1012; CH3+ t-C4H9, k=(12.8 ± 1.1)× 1012. Mutual reaction rate constants and absorption cross-sections for these radicals have also been measured in the same system. The values obtained are (k in cm3 mol–1 s–1 and σ in cm2 molecule–1): CH3, k=(20.8 = 0.8)× 1012 and σ=(30.8 ± 0.8)× 10–18; C2H5, k=(10.2 ± 0.9)× 1012 and σ=(1.89 ± 0.10)× 10–18; C3H7, k=(6.78 ± 0.58)× 1012 and σ=(3.89 ± 0.19)× 10–18; t-C4H9, k=(4.96 ± 0.20)× 1012 and σ=(7.47 ± 0.24)× 10–18. Combining these results with the appropriate disproportionation-combination ratios gives values for the corresponding combination and disproportionation rate constants, and cross-reaction and cross-combination ratios have been evaluated. An evaluation of the data for i-C3H7+ i-C3H7 leads to k=(6.69 ± 2.14)× 1012 cm3 mol–1 s–1 being recommended as the best value for the overall rate constant in the temperature range 300–400 K.