Rate coefficients and Arrhenius parameters for the reaction of the NO3 radical with acetaldehyde and acetaldehyde-1d

Rate coefficients for the reaction between NO3 and acetaldehyde have been determined by the absolute rate fast-flow-discharge technique and by the relative rate method. The flow-tube experiments were carried out under pseudo-first-order conditions in NO3 over the temperature range 263–363 K using He as a carrier gas. The data suggests an activation energy of Ea/R = 1950 ± 290 K and k296 = (9.1 ± 0.8) × 10−15 cm3 molecule−1 s−1 (3 σ errors) as an upper limit. Mixing ca. 20% of oxygen in the He carrier gas resulted in Ea/R = 2020 ± 260 K and k296 = (2.5 ± 0.5) × 10−15 cm3 molecule−1 s−1. The relative rate experiments, performed in a static reactor employing long path FTIR detection, gave k298 = (2.62 ± 0.29) × 10−15 cm3 molecule−1 s−1, and showed a moderate kinetic isotope effect, kCH3CHO+NO3/kCH3CDO+NO2 = 2.37 ± 0.08 at 298 K. The differences in the reaction rate coefficients obtained by the two methods are analysed and discussed in terms of secondary reactions involving NO3 in the flow-tube. Model studies indicate that acetyl and peroxyacetyl radicals react with NO3 with rate coefficients of 2.5 × 10−11 and 1.5 × 10−13 molecule cm−3 s−1 at 296 K and 5 mbar, respectively. The reaction was also studied by quantum mechanical methods and the transition states for the abstraction of aldehydic and methylic hydrogen atoms were located. Their relative energies, calculated on the MP2/cc-pVDZ//CCSDT/cc-pVDZ level, conform to the reaction proceeding entirely through Hald-abstraction at room temperature.