Pressure Stabilization of Criegee Intermediates Formed from Symmetric trans-Alkene Ozonolysis

We explore the pressure dependence of a stabilized Criegee Intermediate (sCI) formation from a sequence of trans-alkene ozonolysis reactions. To study the effect of carbon chain length on the stabilization, we select five symmetric trans-alkenes ranging from trans-2-butene (C ₄ ) through trans-7-tetradecene (C ₁₄ ). We measure the pressure falloff curves for each alkene from 50 to 900 Torr in a flow reactor using conversion of SO ₂ to H ₂ SO ₄ with and without an OH scavenger, and subsequent detection of H ₂ SO ₄ with a nitrate chemical ionization mass spectrometer to constrain sCI yields. As the length of the carbon chain increases, we observe a systematic increase in Criegee Intermediate stabilization at a given pressure, along with a systematic decrease in the low-pressure limit. Our results also suggest that for these symmetrical systems the anticonformer of the Criegee Intermediate stabilizes before (at lower pressure than) the syn conformer.