Time-resolved, broadband UV-absorption spectrometry measurements of Criegee intermediate kinetics using a new photolytic precursor: unimolecular decomposition of CH₂OO and its reaction with formic acid

Abstract

We present a time-resolved broadband cavity-enhanced UV-absorption spectrometer apparatus that we have constructed and utilized for temperature- and pressure-dependent kinetic measurements of formaldehyde oxide (CH2OO) reactions.

Solving the discrepancy between the direct and relative-rate determinations of unimolecular reaction kinetics of dimethyl-substituted Criegee intermediate (CH3)2COO using a new photolytic precursor

“…Experiments were performed using a time-resolved, broadband, cavity-enhanced absorption spectrometer (TR-BB-CEAS) apparatus that is schematically shown in Figure 1 and has been described previously. 19 Acetone oxide was produced homogeneously along the reactor by photolysis of (CH 3 ) 2 CIBr at 213 nm in presence of O 2 ([O 2 ] » [(CH 3 ) 2 CI]).…”

Functionalized Hydroperoxide Formation from the Reaction of Methacrolein-Oxide, an Isoprene-Derived Criegee Intermediate, with Formic Acid: Experiment and Theory

“…For example, the reactions of water vapor with syn-MVK-oxide and anti-MACR-oxide were found to be substantially slower than found for alkyl-substituted Criegee intermediates with similar carbon backbones and conformational forms that lack resonance stabilization [12,34]. In contrast, the rate coefficients for reaction of syn-MVK-oxide with formic acid and SO 2 are as large as those for Criegee intermediates such as CH 2 OO [12,14,44,45]. While the barriers for these reactions are comparatively higher than for CH 2 OO, they are strongly submerged relative to reactants such that the rate coefficients for reaction are not greatly impacted.…”

Estimation of mechanistic parameters in the gas-phase reactions of ozone with alkenes for use in automated mechanism construction

“…Calvert et al, 2000). Recent theoretical (Nguyen et al, 2015;Stone et al, 2018;Peltola et al, 2020) works suggest that the only reaction pathway of the bis-oxy radical important under tropospheric conditions is isomerisation to 'hot' formic acid, followed by decomposition to either H2 + CO2 or H2O + CO, in agreement with experimental and theoretical work on acid pyrolysis experiments (Chang et al, 2007;Vichietti et al, 2017). Due to the large excess energy and its small size, very little of the hot acid is stabilised, with measured HCOOH yields from ethene ozonolysis < 5% (Calvert et al, 2000) (and the latter may be due to bimolecular reactions of SCI rather than stabilisation of the hot acid).…”

“…Due to the large excess energy and its small size, very little of the hot acid is stabilised, with measured HCOOH yields from ethene ozonolysis < 5% (Calvert et al, 2000) (and the latter may be due to bimolecular reactions of SCI rather than stabilisation of the hot acid). Stone et al (2018) and Peltola et al (2020) considered the decomposition of stabilised CH2OO using master equation simulations, determining the major decomposition channel to be H2+CO2 (64 % and 61% respectively), with the H2O+CO accounting for the remainder (36%) in Stone et al (2018), while Peltola et al ( 2020) also found a small contribution (~8%) from the OH+HCO channel. It is noted that previous experimental work on ethene ozonolysis (Su et al, 1980;Horie et al, 1991;Neeb et al, 1998) has generally inferred a preference for the H2O+CO channel.…”

“…The unimolecular decomposition rate of stabilised CH2OO has been experimentally determined to be very slow (<12 s -1 ) (Berndt et al, 2015;Chhantyal-Pun et al, 2015;Newland et al, 2015;Stone et al, 2018;Peltola et al, 2020), with a current recommendation by IUPAC of ≤ 0.2 s -1 at 1 bar and 298 K (Cox et al, 2020). Even at the upper end of these estimates, decomposition is a negligible atmospheric fate for stabilised CH2OO compared to reaction with water vapour.…”