MECHANISMS AND RATES OF THE REACTIONS C{sub}2H{sub}5+O AND 1-C{sub3H{sub}7+ O

摘要

The mechanisms and rates of the reactions of the primary alkyl radicals ethyl and l-propyl with oxygen atoms at room temperature and low pressure (around 5 mbar) have been studied using two independent experimental arrangements. The reactants were generated by UV-laser flash photolysis with different precursors (C{sub}2H{sub}5COC{sub}2H{sub}5, C{sub}2H{sub}6+CFCl{sub}3, C{sub}2H{sub}5I, C{sub}3H{sub}7COC{sub}3H{sub}7, SO{sub}2). Stable species concentrations were measured quantitatively by Fourier transform IR and OH radical concentrations of the ground (v = 0) and first vibrational (v = 1) state by time-resolved laser-induced fluorescence. For both reaction 1 and reaction 2, the mechanism is explained in terms of the formation and subsequent decomposition of a chemically activated alkoxy radical and a competing abstraction channel leading directly to OH and the alkene: C{sub}2H{sub}5+O→C{sub}2H{sub}5O* (reaction 1a)/C{sub}2H{sub}5O*→HCHO+CH{sub}3 (reaction la{sub}1)/ CH{sub}3CHO+H (reaction la{sub}2)//C{sub}2H{sub}5+O→C{sub}2H{sub}4 +OH (reaction 1b). The absolute branching ratio was determined preferentially using diethyl ketone as the C{sub}2H{sub}5 radical source leading to (1a{sub}1)/(1a{sub}2)/(1b), 32/44/24. Relative branching ratios for the C{sub}2H{sub}5 radical sources C{sub}2H{sub}6+Cl and C{sub}2H{sub}5I were derived as (1a{sub}1)/(1a{sub}2)=1/1.5 and 1/1.55, respectively. The overall rate coefficient of the reaction C{sub}2H{sub}5+ O was measured as k{sub}1=(1.04±0.1)×10{sup}14 cm{sup}3 mol{sup}-1 s{sup}-1 and in addition k(C{sub}2H{sub}5+OH)=(7.0±1)×10{sup}13 cm{sup}3 mol{sup}-1 s{sup}-1. The mechanism and the rate of reaction 2 were found as 1-C{sub}3H{sub}7 +O→1-C{sub}3H{sub}7O* (reaction 2a)/ 1-C{sub}3H{sub}7O*→ HCHO+C{sub}2H{sub}5 (reaction 2a{sub}1)/C{sub}2H{sub}5CHO+H (reaction 2a{sub}2)//1-C{sub}3H{sub}7+O→C{sub}3H{sub}6+OH (reaction 2b) (branching ratio (2a{sub}1)/(2a{sub}2)/(2b), 44/ 32/ 24) and k{sub}2= (8.2±1)×10{sup}13 cm{sup}3 mol{sup}-1 s{sup}-1. The results are discussed in terms of statistical rate theory.