Direct measurement of Criegee intermediate (CH2OO) reactions with acetone, acetaldehyde, and hexafluoroacetone

Abstract

Criegee biradicals, i.e., carbonyl oxides, are critical intermediates in ozonolysis and have been implicated in autoignition chemistry and other hydrocarbon oxidation systems, but until recently the direct measurement of their gas-phase kinetics has not been feasible. Indirect determinations of Criegee intermediate kinetics often rely on the introduction of a scavenger molecule into an ozonolysis system and analysis of the effects of the scavenger on yields of products associated with Criegee intermediate reactions. Carbonyl species, in particular hexafluoroacetone (CF(3)COCF(3)), have often been used as scavengers. In this work, the reactions of the simplest Criegee intermediate, CH(2)OO (formaldehyde oxide), with three carbonyl species have been measured by laser photolysis/tunable synchrotron photoionization mass spectrometry. Diiodomethane photolysis produces CH(2)I radicals, which react with O(2) to yield CH(2)OO + I. The formaldehyde oxide is reacted with a large excess of a carbonyl reactant and both the disappearance of CH(2)OO and the formation of reaction products are monitored. The rate coefficient for CH(2)OO + hexafluoroacetone is k(1) = (3.0 ± 0.3) × 10(-11) cm(3) molecule(-1) s(-1), supporting the use of hexafluoroacetone as a Criegee-intermediate scavenger. The reactions with acetaldehyde, k(2) = (9.5 ± 0.7) × 10(-13) cm(3) molecule(-1) s(-1), and with acetone, k(3) = (2.3 ± 0.3) × 10(-13) cm(3) molecule(-1) s(-1), are substantially slower. Secondary ozonides and products of ozonide isomerization are observed from the reactions of CH(2)OO with acetone and hexafluoroacetone. Their photoionization spectra are interpreted with the aid of quantum-chemical and Franck-Condon-factor calculations. No secondary ozonide was observable in the reaction of CH(2)OO with acetaldehyde, but acetic acid was identified as a product under the conditions used (4 Torr and 293 K).

Reactivity of stabilized Criegee intermediates (sCIs) from isoprene and monoterpene ozonolysis toward SO<sub>2</sub> and organic acids

“…Berndt et al (2014a) also showed that significant differences in the relative rate coefficients k(sCI + H 2 O) / k(sCI + SO 2 ) occurred between syn-and anti-confomers of sCI from trans-2-butene. Absolute measurements by Taatjes et al (2012) support this finding as well.…”

“…Due to the relatively long lifetime of sCI, bimolecular reactions of sCIs with several compounds like water vapour, SO 2 , carbonyls, organic acids, etc., are also possible (e.g. Neeb et al, 1996Neeb et al, , 1997Johnson, 2001;Welz et al, 2012Welz et al, , 2014Mauldin III et al, 2012;Berndt et al, 2012Berndt et al, , 2014aTaatjes et al, 2012Taatjes et al, , 2013. These reactions can potentially be fast enough to contribute significantly to the atmospheric oxidation capacity.…”

“…An extremely high reactivity of CH 2 OO and CH 3 CHOO toward formic (HCOOH) and acetic acid (CH 3 COOH) was observed also by Welz et al (2014) in a low-pressure system. Also Taatjes et al (2012; showed that sCIs -at least the simple sCIs -are reactive toward other trace gases in addition to SO 2 . These observations imply that reactions of sCI with organic acids might have atmospheric importance, and further research is urgently required.…”

Reactions between Criegee Intermediates and the Inorganic Acids HCl and HNO3: Kinetics and Atmospheric Implications

“…[3,10] Stabilized CIs react quickly (~10 -12 -10 -10 cm 3 s -1 ) with many trace atmospheric gases. [8,[11][12][13][14] Under humid conditions, reaction with SO2 leads to H2SO4 which catalyzes growth of atmospheric aerosol particles. [4,[15][16][17][18] The steady state concentrations of CIs in the atmosphere are limited by reactions with scavengers, the most important of which is water vapor.…”

Night-time measurements of HO<sub><i>x</i></sub> during the RONOCO project and analysis of the sources of HO<sub>2</sub>

“…Stabilised CIs (SCIs) are known to react with a variety of compounds, including H 2 O, NO 2 , SO 2 , and a variety of organic compounds (e.g. Mauldin III et al, 2012;Taatjes et al, 2012Taatjes et al, , 2013Taatjes et al, , 2014Ouyang et al, 2013;Stone et al, 2014a). There is experimental evidence for the formation of OH from the thermal decomposition of SCIs, on a much longer timescale than the decomposition or isomerisation of excited CIs (Kroll et al, 2001a, b).…”