Pressure Dependence of Butyl Nitrate Formation in the Reaction of Butylperoxy Radicals with Nitrogen Oxide

Abstract

The yield of 1- and 2-butyl nitrates in the gas-phase reactions of NO with n-C4H9O2 and sec-C4H9O2, obtained from the reaction of F atoms with n-butane in the presence of O2, was determined over the pressure range of 100-600 Torr at 298 K using a high-pressure turbulent flow reactor coupled with a chemical ionization quadrupole mass spectrometer. The yield of butyl nitrates was found to increase linearly with pressure from about 3% at 100 Torr to about 8% at 600 Torr. The results obtained are compared with the available data concerning nitrate formation from NO reaction with other small alkylperoxy radicals. These results are also discussed through the topology of the lowest potential energy surface mainly obtained from DFT(B3LYP/aug-cc-pVDZ) calculations of the RO2 + NO reaction paths. The formation of alkyl nitrates, due essentially to collision processes, is analyzed through a model that points out the pertinent physical parameters of this system.

Atmospheric Fate of Methyl Vinyl Ketone: Peroxy Radical Reactions with NO and HO2

“…This mechanism proceeds following destabilization of the ROONO moiety. In some cases, the nascent radicals do not separate but rather reform an activated RONO 2 complex, which then undergoes collisional stabilization to form the nitrate. − As such, the yield will depend on the lifetime of the complex. This general mechanism is consistent with findings that alkyl nitrate yields tend to increase with the size of molecule and decrease with increasing temperature .…”

Barrierless Reactions with Loose Transition States Govern the Yields and Lifetimes of Organic Nitrates Derived from Isoprene

“…38 In more recent work, Butkovskaya et al suggested that a weakly bound adduct leads to both the formation of NO 2 and butyl nitrate although the structure was not optimized. 32 The identification of the vdW complex and the transition state leading to the organic nitrate in this study permits the quantification of the isoprene organic nitrate yield because the product distribution is acutely sensitive to the vdW energy relative to the barriers leading to NO 2 and RONO 2 .…”

“…Significantly, this species is common to both trajectories, and its identification here helps to rationalize the behavior of excited peroxynitrites, as will be discussed below. At this stage, the vdW complex may fragment completely using 4.2 kcal/mol of energy to generate the alkoxy radical and NO 2 , or the NO 2 may rotate so that the nitrogen faces the alkoxy radical to produce the organic nitrate with a concomitant release of energy, as discussed by Butkovskaya et al 32 The latter process possesses a minute barrier relative to complete vdW dissociation. This is consistent with the results of Zhang and co-workers, 13 which have indicated that the barrier to organic nitrate formation must be less than alkoxy radical production in order to observe increased alkoxy radical production at higher temperatures.…”

“…55 both NO 2 and butyl nitrate, although the structure was not optimized. 32 The identification of the vdW complex and the transition state leading to the organic nitrate in this study permits quantification of the isoprene organic nitrate yield because the product distribution is acutely sensitive to the vdW energy relative to the barriers leading to NO 2 and RONO 2 . Interestingly, Figure 2 displays three exit channel reactions: (1) alkoxy radical + NO 2 , (2) organic nitrate, and (3) a vdW complex involving methyl vinyl ketone, hydrogenated formaldehyde radical, and NO 2 .…”

“…For example, Butkovskaya et al. used density functional theory (DFT) methods to compute the potential energy surface (PES) for the reaction of butylperoxy radicals with NO and used a collisional model to explain organic nitrate formation . Other computational studies invoking density functional methods and the master equation formalism to describe the vibrationally excited peroxynitrite intermediates of isoprene have not identified transition state structures for the exit channels. , Without the structures and energies serving as constraints in solving the master equation, they simply become adjustable parameters that may be varied in fitting experimental data.…”