Experimental Study of the Kinetics of the Reaction of Acetic Acid with Hydroxyl Radicals from 255 to 355 K

Abstract

The rate constant of the reaction of OH with acetic acid over the temperature range of 255-355 K was determined using our High-Pressure Flow System with laser-induced fluorescence detection of the OH radicals and FTIR spectrometry for acetic acid quantification. The rate constant displays a negative temperature dependence and can be described by the Arrhenius expression: k(1)(T) = (5.38 +/- 0.28) x 10(-14) exp(740 +/- 51/T) cm(3) molecule (-1) s(-1), with k(1) = (6.77 +/- 0.14) x 10(-13) cm(3) molecule (-1) s(-1) at 295 K. The negative temperature dependence suggests a pre-reactive complex formation between the OH radicals and the acetic acid monomer, and this result is consistent with previous reports. The use of FTIR spectrometry allows for separation of the acetic acid monomer and dimer in the spectrum and gives a measurement of the acetic acid monomer that is independent of the temperature measurement and free of reliance on an equilibrium constant expression that can introduce high uncertainty. The highly sensitive laser-induced fluorescence for OH detection coupled with the FTIR spectrometry result in a rate constant measurement with low uncertainty, and the data set presented here in the temperature range of 255-355K serves to bridge existing data sets that are obtained either above or below room temperature.