Temperature-dependent rate coefficient measurements for the reaction of bromine atoms with a series of aldehydes

Relative rate coefficient data have been obtained for the reactions Br + RCHO --> RCO + HBr for a series of aldehydes: HCHO, reaction (1); CH3CHO, reaction (2); CH3CH2CHO, reaction (3); CH3CH2CH2CHO, reaction (4). Measurements were made over the temperature range 240-300 K in an environmental chamber/FTIR spectrometer system, using standard relative rate techniques. All measured rate coefficient ratios were found to be independent of temperature over the range studied (k(2)/k(1) = 3.60 +/- 0.29, k(3)/k(1) = 6.65 +/- 0.53, k(4)/k(1) = 8.62 +/- 0.69, and k(3)/k(2) = 1.80 +/- 0.14), implying that the activation barriers for all four reactions are essentially identical with the A-factors increasing with the size of the aldehyde. Relative rate coefficients for k(1) and k(2) agree well with currently recommended data at room temperature, but inconsistencies on the order of 20% arise at lower temperatures. The entire set of relative rate coefficient measurements is put on an absolute scale using a combination of currently recommended values for k(1) and k(2). The following expressions (all in units of cm(3) molecule(-1) s(-1)) are obtained: k(1) = (0.79 +/- 0.10) x 10(-11) exp(-580 +/- 200/T), k(2) = (2.7 +/- 0.4) x 10(-11) exp(-567 +/- 200/T), k(3) = (5.75 +/- 0.75) x 10(-11) exp(-610 +/- 200/T), k(4) = (5.75 +/- 0.75) x 10(-11) exp(-540 +/- 200/T), where uncertainties quoted for the A-factor reflect the uncertainty in the room temperature value. (C) 2000 John Wiley & Sons, Inc