Abstract
Criegee intermediates play important roles in atmospheric chemistry. Methyl Criegee intermediate, CH3CHOO, has two conformers, syn- and anti-conformers. Syn-CH3CHOO would undergo fast unimolecular decomposition to form OH radical via 1,4 H-atom transfer. In this work, unimolecular decomposition of syn-CH3CHOO was probed in real time with UV absorption spectroscopy at 278–318 K and 100–700 torr. We used water vapor as the scavenger of anti-CH3CHOO to distinguish the absorption signals of the two conformers. After removing the contributions from reactions with radical byproducts, reaction with water vapor and wall loss, we obtained the unimolecular reaction rate coefficient of syn-CH3CHOO (at 300 torr), which increases from (67 ± 15) s−1 at 278 K, (146 ± 31) s−1 at 298 K, to (288 ± 81) s−1 at 318 K with an Arrhenius activation energy of ca. 6.4 kcal mol−1 and a weak pressure dependence for 100–700 torr. Compared to previous studies, this work provides temperature dependent unimolecular rates of syn-CH3CHOO at higher pressures, which are more relevant to atmospheric conditions.
Highlights
Criegee intermediates are very reactive carbonyl oxides formed in the reactions of ozone with alkenes and play important roles in atmospheric chemistry, including oxidation of water, SO2, NOx, etc
CH2OO and anti-CH3CHOO react with water vapor very quickly but syn-CH3CHOO and (CH3)2COO react with water vapor much slower
If we focus on the unimolecular rate coefficients of syn-CH3CHOO reported a er 2012, the reported experimental value[9,10,11,12] at 298 K ranges from 3 to 300 sÀ1 whilst the reported theoretical value[13,14,15] is from 24 to 330 sÀ1.1 Unimolecular rates may control the steady-state concentrations and the impact of such a Criegee intermediate in the atmosphere
Summary
Criegee intermediates are very reactive carbonyl oxides formed in the reactions of ozone with alkenes (ozonolysis) and play important roles in atmospheric chemistry, including oxidation of water, SO2, NOx, etc. CHOO20 and directly monitored the kinetics of syn-CH3CHOO via its strong UV absorption in real time.[21] The unimolecular rates were determined at atmospherically relevant temperatures and pressures.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
