Stopped-flow studies of the mechanisms of ozone-alkene reactions in the gas phase: tetramethylethylene

Abstract

CH3)C(=0)CH2' radical as well as the accompanying HO' radical was formed in the 03-TME system via reaction 5.To further examine the oxidation of CH3C(=0)CH2' radicals, the photolysis of mixtures containing parts-per-million concentrations of Cl2 and (CH3)2C=0 in air yielded methylglyoxal H3C(=0)CH0 as a major product, i.e., ca. 30% of A-[(CH3)2C=0], which can be attributed to the oxidation of the CH3C(=0)CH2' radical. Thus, the observation of CH3C(= OjCHO in the 03-TME-02 system (cf. Tables I and II) is consistent with the formation of this radical via reaction 5. A plausible mechanism for the formation of CH3C(=0)CH0 is CH3C(=0)CH2' 4-02 -CH3C(=0)CH200'; 2CH3C(=0)-CH200' -2CH3C(=0)CH20' 4-02; and CH3C(=0)CH20' 4-02 -* CH3C(=0)CH0 4-HOO'. Under atmospheric conditions, CH3C(=0)CH20' may react predominantly with 02 rather than undergoing unimolecular dissociation to CH3CO" and HCHO.12 No further quantitative determination of these competing reactions was pursued in the present study. Instead, at-tention was focused on the detection of a carbonyl product arising from the reaction CH3C(=0)CH200' 4-HOO* -CH3C(= 0)CH2OOH 4-02, since this compound was suspected to be the unidentified species exhibiting the C=0 band at ca. 1740 cm'1 in the 03-TME reaction (cf. Figure 2C). A broad band in this

Atmospheric isoprene ozonolysis: impacts of stabilised Criegee intermediate reactions with SO<sub>2</sub>, H<sub>2</sub>O and dimethyl sulfide

“…This is likely to be a significant atmospheric sink for syn-SCIs because of their slow reaction with water vapour. Previous studies have identified the hydroperoxide rearrangement as dominant for SCIs with a syn configuration, determining their overall unimolecular decomposition rate (Niki et al, 1987;Rickard et al, 1999;Martinez and Herron, 1987;Johnson and Marston, 2008). This route has been shown to be a substantial non-photolytic source of atmospheric oxidants (Niki et al, 1987;Alam et al, 2013).…”

Atmospheric isoprene ozonolysis: impacts of stabilized Criegee intermediate reactions with SO<sub>2</sub>, H<sub>2</sub>O and dimethyl sulfide

“…Previous studies have identified the hydroperoxide rearrangement as dominant for SCIs with a syn configuration, determining their overall unimolecular decomposition rate (Niki et al, 1987;Rickard et al, 1999;Martinez and Herron, 1987;Johnson and Marston, 2008). This route has been shown to be a substantial non-photolytic source of atmospheric oxidants (Niki et al, 1987;Alam et al, 2013).…”

The atmospheric impacts of monoterpene ozonolysis on global stabilised Criegee intermediate budgets and SO<sub>2</sub> oxidation: experiment, theory and modelling

“…. Unimolecular reactions of syn-CI/-SCIs are dominated by a 1,4-H shift, forming a vinyl hydroperoxide (VHP) intermediate (Niki et al, 1987;Rickard et al, 1999;Martinez and Herron, 1987;Johnson and Marston, 2008;Kidwell et al, 2016). Decomposition of the VHP formed in this process is an important non-photolytic source of OH, HO 2 and RO 2 in the atmosphere (Niki et al, 1987;Alam et al, 2013;Kidwell et al, 2016), which can also lead to secondary organic aerosol formation (Ehn et al, 2014).…”