Absorption cross-sections and mutual reaction rate constants for C2H5 and t-C4H9 radicals

Abstract

Molecular modulation spectrometry has been used to measure the absorption cross-sections and mutual reaction rate constants for C₂H₅ and t-C₄H₉ radicals in the temperature ranges 301–373 and 300–421 K, respectively. The values obtained are: for C₂H₅ radicals, σ=(2.06 ± 0.22)× 10^–18 cm² molecule^–1 and k=(1.12 ± 0.19)× 10¹³ cm³ mol^–1 s^–1; for t-C₄H₉ radicals, σ=(7.36 ± 0.39)× 10^–18 cm² molecule^–1 and, at 300–308 K, k=(5.28 ± 0.40)× 10¹² cm³ mol^–1 s^–1. The rate constant for the t-C₄H₉ reaction shows a strong negative temperature dependence, confirming the observation made previously by Parkes and Quinn. Combining these rate constants with the appropriate disproportionation–combination ratios gives values for the corresponding recombination and disproportionation rate constants. These results are compared with those available in the literature, and best values for the recombination rate constant for both C₂H₅ and t-C₄H₉ are recommended.