Product distributions form the OH radical-induced oxidation of but-1-ene, methyl-substituted but-1-enes and isoprene in NO_x-free air

摘要

Product distributions resulting from the OH-induced oxidation of but-1ene, 2-methylbut-1-ene, 3-methylbut-1-ene and isoprene in air were measured i nthe absence of nitrogen oxides and compared with predictions based on currently accepted oxidation mechanisms. In the case of butenes, the observed distributios of carbonyl compounds, hydroxyketones, hydroxyalkanals and diols were evaluated to obtain probatilities for the initial attack of OH radical on the outer position of the double bond(#gamma#=0.90+-0.03 for 2-Me-but-1-ene and #gamma#-0.76+-0.05 for both but-1ene and 3-Me-but-1-ene), for the probability of formation of stable products in the self-reaction of secondary #beta#-hydroxyperoxyl radicals (K_(ssb)/K_(SS)=0.29+-0.07 for but-1-ene and K_(ssb)/K_(ss)=0.19+-0.06 for 3-Me-but-1-ene), and for the ratio of the reaction with oxygen vs. decomposition of #beta#-hydroxyalkoxyl radicals, K_3[O_2]/(K_4 + k_3[O_2])= 0.25+-0.04 for but-1-ene and = 0.38 +- 0.04 for 3-Me-but-1-ene. The last two values disagree with other published data, which suggest a smaller effet of oxygen. The oxidation of isoprene produced methacrolein and methyl vinyl ketone with a ratio 0.93+-0.10, the ratio of methyl vinyl ketone and 3-methylfuran was 7.3+-1.0. Other products were 1-hydroxy-3-methylbut-3-n-2-one distribution was complex and could not be fully elucidated. Computer simulations based on several mechanisms applied the relative probabilities for OH addition found fro the but-1-enes. Comparison with the experimental data suggests probabilities for OH additon to the methylated double bond of 0.504+-0.027 (outer position) and 0.056+-0.003(inner position), and to the non-methylated double bond of 0.335+-0.023 (outer position) and 0.015+--0.008(inner position)