Gas-phase reactions of the nitrate radical with olefins

Abstract

Reactions of the Nitrate Radical with Olefins 1629 eter for an 0NC1-Ar collision is taken to be 4,09 Á then eq 5 becomes eq 6. The values of 2&lp and &2nd order are shown kLp = 1.76856 X 1017T-1/2 eXp(-38,000/RT) cc/mol sec (6)in Table II. The correspondence between the calculated and the experimental values especially at the higher temperatures is quite satisfying considering the simplicity of the approach. This correspondence is strong indication that under the present conditions in the shock tube the decomposition is proceeding essentially by the unimolecular (free radical) pathway. A further check on this conclusion is provided by a comparison of the values of the half-lives for reaction by the unimolecular (free radical) and bimolecular (molecular) pathways. A calculation using the rate constant expression of Ashmore and Burnett30 establishes that under present conditions the half-life of the molecular pathway is three orders of magnitude longer than the halflife of the free-radical pathway. This evidence then shows that ONC1 is decomposing by means of a unimolecular mechanism and that under present conditions (i.e., high dilution in argon) it is at or near low pressure conditions.

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II – gas phase reactions of organic species

“…The preferred 298 K rate coefficient is in reasonable agreement with the relative rate measurements of , Japar and Niki (1975) and when the differing values of the equilibrium constant used for the N 2 O 5 ↔NO 3 +NO 2 reactions are taken into account, and considering the uncertainties in this equilibrium constant. (Bandow et al, 1980;Shepson et al, 1985; …”

Reevaluation of the rate constant for the reaction propene + NO3 by absolute rate determination

“…However, this work does not agree with the other three determinations from Japar and Niki [9], Atkinson et al [12], and Canosa-Mas et al [7] and with the IUPAC and JPL recommendations that are about 50% higher. As indicated in the introduction, the same group [8,9] has published two values of k 4 in disagreement while they were using the same technique and no explanation was proposed by the authors. Similarly, Atkinson and coworkers have also published two studies on this rate constant.…”

“…One can observe that our determination is in good agreement with the lowest three values published by Morris and Niki [8] and Atkinson et al [10]. However, this work does not agree with the other three determinations from Japar and Niki [9], Atkinson et al [12], and Canosa-Mas et al [7] and with the IUPAC and JPL recommendations that are about 50% higher. As indicated in the introduction, the same group [8,9] has published two values of k 4 in disagreement while they were using the same technique and no explanation was proposed by the authors.…”

“…One can also notice that rate constants published by Atkinson et al [10,12] are significantly different, but no explanation was given by the authors. A similar disagreement is observed for two data published by another group [8,9] that remains also unexplained. Hence, it appears that new absolute rate determination is needed.…”

“…In this study, NO 3 decay consecutive to its reaction with propene was measured using its visible absorption at 662 nm in a discharge-flow tube. In the studies [7,9,12] is in good agreement, whereas another consistent set of three other data [8,10] is significantly lower. One can also notice that rate constants published by Atkinson et al [10,12] are significantly different, but no explanation was given by the authors.…”