Modeling the Organic Nitrate Yields in the Reaction of Alkyl Peroxy Radicals with Nitric Oxide. 2. Reaction Simulations

Abstract

Master equation calculations are used to model gas-phase literature experimental data for alkyl nitrate formation via the following reaction system of reversible reactions: (1) RO2 + NO ↔ ROONO, (2) ROONO ↔ RO + NO2, (3) ROONO ↔ RONO2, and (4) RONO2 ↔ RO + NO2 for R = CH3, i-C3H7, and 2-C5H11. The structures and thermochemistry of the stable species are based on electronic structure calculations described in the preceding companion paper in this issue (Lohr et al. J. Phys. Chem. A 2003, 107, xxx−xxx). Literature data for recombination rate constants are used to constrain the model calculations. Several transition state models and a range of energy transfer parameters are investigated. The results for R = CH3 show that a wide variety of plausible transition state models for k - 4 gives good agreement with experiment for reaction (−4), because changes in assumed energy transfer parameters can compensate for differences between the transition state models. It is concluded that recombination reactions are good sources of absolute energy transfer parameters only when transition state properties are known with great accuracy. Although satisfactory models are obtained for the individual systems, the parameters cannot be transferred reliably from one system to another. Master equation models can be made to reproduce the experimental 2-pentyl nitrate yields from the title reaction as long as 〈Δ E〉down, the average energy transferred in deactivating collisions, is assumed to be surprisingly, and perhaps unphysically, small (∼25 cm-1), regardless of assumptions about the barrier to isomerization reaction 3. Several critical assumptions in the master equation models are examined, but none of them accounts for the small value of 〈Δ E〉down. It is concluded that new experiments should be carried out to verify or possibly revise the pressure-dependent alkyl nitrate yield data currently available in the literature.

The production of organic nitrates from various anthropogenic volatile organic compounds

“…Ozone in the troposphere is formed from the OH oxidation of VOCs in the presence of NO. The peroxy radicals formed from reaction of OH with the VOCs (each with an efficiency, α) react with NO, to form an unstable peroxy nitrite adduct [5,6] (reaction (2)). This adduct can then dissociate (reaction (3a)) or stabilize (reaction (3b)) to form organic nitrates.…”

The production of organic nitrates from atmospheric oxidation of ethers and glycol ethers

“…Under the conditions of this experiment (in the presence of NO x ), the chemistry in the reaction chamber is such that the VOC will react only with OH and the resulting peroxy radical will react exclusively with NO, forming an unstable adduct [10,26,27], ROONO * . In general, reaction between RO and NO 2 to yield the same organic nitrate as the RO 2 + NO reaction is very slow, relative to the reaction between RO and O 2 .…”

“…The peroxy radicals react with NO to form an unstable peroxy nitrite adduct (reaction (2)), which can dissociate (reaction 3a) or stabilize (reaction (3b)) to form an organic nitrate. This process may also occur [10] in part through formation of a vibrationally excited nitrate that can be stabilized, or dissociate to produce the same products as in reaction (3a).…”

<i>α</i>-Pinene nitrates: synthesis, yields and atmospheric chemistry

“…RO 2 reaction with NO forms an unstable peroxy nitrite intermediate [ROONO * ] that decomposes into NO 2 and RO· (Reaction R5) or, less often, will rearrange to form a stable organic nitrate (Reaction R4) (Atkinson et al, 1982;Barker et al, 2003;Monks et al, 2009). The organic nitrate, RONO 2 , formed from Reaction R4 can serve as a reservoir of NO x in the atmosphere.…”