Hydrogen Abstraction Probability in Reactions of Gas-Phase NO₃ with an OH-Functionalized Organic Surface

Abstract

Interfacial collisions between gas-phase nitrate radicals and a model organic surface have been investigated to determine the initial reaction probability. Model surfaces were created by the spontaneous adsorption of HO-terminated alkanethiols (HS(CH 2 ) 15 CH 2 OH) at a polycrystalline gold substrate. The experimental approach employed in situ reflection−absorption infrared spectroscopy (RAIRS) to monitor bond rupture and formation, while a well-characterized effusive flux of NO 3 impinges on the organic surface. The surface reaction kinetics derived from RAIRS measurements revealed that the consumption of the terminal hydroxyl groups was strongly correlated to the formation of a surface-bound nitrate species. The reaction rate and RAIR spectral assignments suggest that the reaction between NO 3 and the HO-SAM is initiated by hydrogen abstraction at the terminal −CH 2 OH groups. The initial reaction probability for hydrogen abstraction at the terminal groups was determined to be (6 ± 1) × 10 −3 . This rate is approximately a factor of 3 greater than the rate of NO 3 reaction on an 18-C vinyl-terminated self-assembled monolayer (SAM) surface, which suggests that oxidation of surface-bound alcohols by nighttime nitrate radicals may occur more readily than nitrate oxidation of unsaturated hydrocarbons.

Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms and organic aerosol

“…The reaction products are expected to be formed via similar pathways as seen in the gas phase, i.e. abstraction of the aldehydic-H atom for aldehydes and abstraction of an H-atom from either the O-H or adjacent α-CH 2 group for alcohols prior to reaction of NO 2 and NO 3 with the ensuing alkyl and peroxy radicals (Zhang and Morris, 2015).…”

Review response

“…For multicomponent liquid particles, the uptake coefficient will also depend on the particle viscosity (Iannone et al, 2011) though it has not been clearly established if the reaction proceeds predominantly at the surface or throughout the particle (Iannone et al, 2011). The reaction products are expected to be formed via similar pathways as seen in the gas phase, i.e., abstraction of the aldehydic-H atom for aldehydes and abstraction of an H atom from either the O-H or adjacent α-CH 2 group for alcohols prior to reaction of NO 2 and NO 3 with the ensuing alkyl and peroxy radicals (Zhang and Morris, 2015).…”

“…The efficiency of uptake of NO 3 to unsaturated acids is comparable to that found with other oxidized, saturated organics (Moise et al, 2002) suggesting that the reaction proceeds, as in the gas phase, via abstraction rather than addition. Significantly larger uptake coefficients have been observed for a range of unsaturated, long-chain acids, with γ often between 0.1 and 1 Knopf et al, 2011;Zhao et al, 2011a). γ depends on the number and position (steric factors) of the double bond.…”

“…For example, the uptake coefficient for abietic acid is a factor of 100 lower than for linoleic acid . The condensed-phase products formed in the interaction of NO 3 with unsaturated acids are substituted carboxylic acids, including hydroxy nitrates, carbonyl nitrates, dinitrates, and hydroxy dinitrates (Hung et al, 2005;Docherty and Ziemann, 2006;McNeill et al, 2007;Zhao et al, 2011a).…”

Supplementary material to "Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms and organic aerosol"

“…Organic nitrates formed simultaneously with loss of terminal CH 2 OH groups. (Zhang and Morris, 2015) Levoglucosan [12] CWFT, (s) ~1.4 (298 K) N4 RH < 0.5 %, O 2 present. (Knopf et al, 2011) (Shiraiwa et al, 2009) Diethyl sebacate (DES) [13] CWFT, (l) 3.5 -4.5 (278-298 K) (Gross and Bertram, 2009) Diethyl sebacate (DES) [14] CWFT, (l) 4.4 ± 0.4 (278 K) (Xiao and Bertram, 2011) Dioctyl sebacate (DOS) [15] CWFT, (l) 3.9 ± 0.3 (278 K) (Xiao and Bertram, 2011) Tridecanal ( CWFT, (l) 290 !!…”