Atmospheric Degradation of 2-Butanol,2-Methyl-2-butanol,and 2,3-Dimethyl-2-butanol:OH Kinetics and UV Absorption Cross Sections

摘要

The absolute rate coefficients for the reactions of hydroxyl radical (OH) with 2-butanol (k_1),2-methyl-2-butanol (k_2),and 2,3-dimethyl-2-butanol (k_3) were measured as a function of temperature (263-354 K) and pressure (41 - 193 Torr of He,Ar,and N_2) by the pulsed laser photolysis/laser-induced fluorescence technique.This work represents the first absolute determination of k_1-k_3 and their temperature dependence.No pressure dependence of the rate coefficients was observed in the range studied.Thus,k_i(298 K) values (x10~(-12) cm~3 molecule~(-1) s~(-1) with an uncertainty of +-2 sigma) were averaged over the pressure range studied yielding 8.77+-1.46,3.64+-0.60,and 9.01+-1.00 for 2-butanol (k_1),2-methyl-2-butanol (k_2),and 2,3-dimethyl-2-butanol (k_3),respectively.k_1 and k_3 exhibit a slightly negative temperature dependence over the temperature range studied.In contrast,the rate coefficient for the reaction of OH with 2-methyl-2-butanol (k_2) did not show any temperature dependence.Some deviation of the conventional Arrhenius behavior was clearly observed for k_3.In this case,the best fit to our data was found to be described by the three-parameter expression k(T)=A+B exp(-C/T).The UV absorption cross sections of 2-butanol,2-methyl-2-butanol,and 2,3-dimethyl-2-butanol have also been measured at room temperature between 208 and 230 nm.The values reported constitute the first determination of the UV cross sections of those alcohols.Our results are compared with previous studies,when possible,and are discussed in terms of the H-abstraction by OH radicals.The atmospheric implications of these reactions and the photochemistry of these alcohols are also discussed.