Kinetics of OH radical reactions with a series of symmetric acetals in the temperature range 293-617 K

Rate constants of the reactions of OH radicals with dimethoxymethane, diethoxymethane and dipropoxymethane have been measured in the temperature range 293-619 K at a total pressure of 100 Torr. The pulse laser photolysis-laser induced fluorescence technique (PLP-LIF) was used with OH radicals produced by photolysis of H2O2 at lambda = 266 nm. Combining data so obtained with recent determinations at lower temperatures shows that, for the three acetals, the Arrhenius plots exhibit a minimum. A three-parameter Arrhenius expression reproduces the minimum but the temperature exponent and the preexponential factor have unrealistic values. For the three reactions, a better description of the temperature dependence was obtained by fitting the rate constant by the sum of two functions corresponding to different reaction pathways at low and high temperature.