Kinetics of the reaction of OH with methyl nitrate (223-343 K)

Rate coefficients (k₄) for the reaction of hydroxyl radicals (OH) with methyl nitrate (CH₃ONO₂) were measured over the temperature range 232-343 K using pulsed laser photolysis to generate OH and pulsed laser-induced fluorescence to detect it in real-time and under pseudo-first-order conditions. In order to optimize the accuracy of the rate coefficients obtained, the concentration of CH₃ONO₂ (the reactant in excess) was measured on-line by absorption spectroscopy at 213.86 nm for which the absorption cross-section was also measured (σ_213.86 = 1.65 ± 0.09 × 10^-18 cm² molecule^-1). The temperature-dependent rate coefficient is described by k₄(T) = 7.5 × 10^-13 exp[(-1034 ± 40)/T] cm³ molecule^-1 s^-1 with a room temperature rate coefficient of k₄(296 ± 2 K) = (2.32 ± 0.12) × 10^-14 cm³ molecule^-1 s^-1 where the uncertainty includes the statistical error of 2σ and an estimation of the potential systematic bias of 5%. This new dataset helps to consolidate the database for this rate coefficient and to reduce uncertainty in the atmospheric lifetime of CH₃ONO₂. As part of this study, an approximate rate coefficient for the reaction of H-atoms with CH₃ONO₂ (k₉) was also derived at room temperature: k₉(298 K) = (1.68 ± 0.45) × 10^-13 cm³ molecule^-1 s^-1.