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.