Low-pressure and nascent yields of stabilized Criegee intermediates CHOO and CHCHOO in ozonolysis of propene.

The yields of stabilized Criegee intermediates (sCIs), both CHOO and CHCHOO, produced from ozonolysis of propene at low pressures (7-16 Torr) were measured indirectly using cavity ringdown spectroscopy (CRDS) and chemical titration with an excess amount of sulfur dioxide (SO). The method of monitoring the consumption of SO as a scavenger and the production of secondary formaldehyde (HCHO) allows characterization of the total sCI and the stabilized CHOO yields at low pressure and in a short residence time. Both the total sCI and the stabilized CHOO yields in the propene ozonolysis were found to decrease with decreasing pressure. By extrapolating the 7-16 Torr measurements to the zero-pressure limit, the nascent yield of the total sCIs was determined to be 25 ± 2%. The ranges of nascent yields of stabilized CHOO and stabilized CHCHOO were estimated to be 20-25% and 0-5%, respectively. The branching ratios of the stabilized and high-energy CHOO* and CHCHOO* were also determined.