A novel long path photolysis cell—application to the reactivity of selected organic compounds toward the nitrate radical (NO3)

Bimolecular rate coefficients for the reactions of the nitrate radical, NO3, with methanol, ethanol, acetaldehyde tert-butyl methyl ether, propionic acid, dimethylmalonate, dimethylsuccinate, dimethyl carbonate and diethylcarbonate in aqueous solutions have been measured using a novel experimental approach. This study was performed using laser flash photolysis (LFP) with a capillary made of Teflon AF2400 as a long path capillary photolysis cell. Taking benefit of this new material allowing a long optical path length for a very limited irradiated solution volume, new rate constants were established. All experiments were carried out at room temperature. Measured rate coefficients for the reaction of the NO3 radical with methanol, ethanol, acetaldehyde, dimethylcarbonate, diethylcarbonate, dimethylmalonate, dimethyl succinate, propionic acid and tert-butyl-methyl ether are (units are 105 M−1 s−1): kNO3 + ethanol = 4.8 ± 0.5, kNO3 + ethanol = 19 ± 3, kNO3 + acetaldehyde = 20 ± 3, kNO3 + dimethylcarbonate = 0.15 ± 0.04, kNO3 + diethylcarbonate = 0.84 ± 0.12, kNO3 + dimethylmalonate = 0.26 ± 0.07, kNO3 + dimethylsuccinate = 0.34 ± 0.02, kNO3 + propionic acid = 0.77 ± 0.02, kNO3 + tert-butyl-methyl ether = 3.9 ± 1.3. The uncertainties in the above expressions are ±2σ and represent precision only. The reported rate coefficients for the reactions of NO3 with methanol, ethanol and acetaldehyde agree well with currently recommended values. To date, there is no kinetic data reported in the literature for the NO3 radical reaction with dimethylcarbonate, diethylcarbonate, dimethylmalonate, dimethylsuccinate, propionic acid and tert-butyl-methyl ether. The reaction mechanism is briefly discussed as a function of bond energies