Kinetics of CH₂OO Reactions with Fluorinated Compounds: Temperature-Dependent Study of CF₃CH=CHCF₃ and Upper Limit Determination for SF₆

Criegee intermediates are highly reactive zwitterionic species formed from alkene-ozone reactions that play important roles in atmospheric oxidation chemistry. This study investigates the kinetics of formaldehyde oxide (CH₂OO) reactions with (E)-1,1,1,4,4,4-hexafluoro-2-butene (CF₃CH=CHCF₃) and sulfur hexafluoride (SF₆) using time-resolved laser-induced fluorescence detection of OH radicals. For the CH₂OO+CF₃CH=CHCF₃ reaction, we measured rate coefficients from 280 K to 323 K at 5–10 Torr, finding values ranging from (1.4±0.3)×10⁻¹⁴ to (3.0±0.5)×10⁻¹⁴ cm³·molecule⁻¹·s⁻¹. The reaction shows positive temperature dependence with an activation energy of (2.7±0.4) kcal/mol. Compared to non-fluorinated alkenes, the fluorinated compound reacts approximately 33 times faster, demonstrating the significant enhancement effect of trifluoromethyl groups. For CH₂OO+SF₆, no measurable reaction was observed at SF₆ concentrations up to 6.5×10¹⁷ molecule·cm⁻³, yielding an upper limit rate coefficient of 7×10⁻¹⁸ cm³·molecule⁻¹·s⁻¹. These results expand the kinetic database for Criegee intermediates reactions with fluorinated compounds and provide insights into atmospheric oxidation pathways involving these species.