The reactions of the branched alkyl radicals iso-butyl and neo-pentyl with oxygen atoms-an experimental and theoretical study

摘要

The reactions of the branched primary alkyl radicals iso-butyl and neo-pentyl radicals with atomic oxygen at room temperature and low pressure have been studied with respect to the mechanism of the multiple reaction channels and the rate coefficients. The primary products and the yield of the reaction channels have been determined by quantitative FTIR spectroscopy using laser flash photolysis for the production of the radicals and atoms (iso-C_4H_(10) + Cl, neo-C_5H_(12) + Cl; Cl from the photolysis of CFCI3, O from SO_2). In an independent experimental arrangement of a conventional discharge flow reactor with molecular beam sampling, the hydrocarbon radicals were detected mass spectrometrically after specific laser induced multiphoton ionization, thus allowing the measurement of the rate coefficients with reference to the reaction C_2H_5 + O(k= 1.04 × 10~(14) cm~3/mols). Both reactions show multichannel behaviour via the formation of a highly excited alkoxy radical followed by C-C and C-H bond cleavage and, in the case of iso-C_4H_9 with a hydrogen atom in the 2-position, a direct abstraction to OH radicals: iso-C_4H_9 + O → iso-C_4H_9O~* iso-C_4H_9O~* → HCHO + 2-C_3H_7 (47+3)% → (CH_3)_2CHCHO + H (28±2)% iso-C_4H_9 + O → (CH_3)_2CCH_2 + OH (25±3)% k_1 iso-C_4H_9 + O) = (8.9 ± 1.6) × 10~(13) cm~3/mols neo-C_5H_(11)+O → neo-C_5H_(11)O~* neo-C_5H_(11)O~* → HCHO + t-C_4H_9 (65 ±4)% → t-C_4H_9CHO + H (34±4)% k_2(neo-C_5H_(11) + O) = (9.7 ± 2.1) × 10~(13) cm~3/mols.