Criegee intermediate formation from photolytic precursors and characterization of LI/MS instrumentation

The reactions of chlorine atoms (·Cl) with several hydrocarbons, methane, dichloromethane, ethane, dimethyl ether, and toluene, have been investigated as a laser photolysis source of Criegee intermediates (CI), which are a class of reactive species normally involved in the ozonolysis of alkenes in the atmosphere. The detection of secondary ozonides (SOZ), using gas chromatography with flame ionization detection and mass spectrometry, has been used as an indicator of stabilized CI production. Methane and ethane were the only precursors that resulted in detection of SOZ with significantly larger SOZ signals from methane. This is the first unequivocal proof that a Criegee intermediate can be produced in the gas phase from a pathway other than ozone-alkene reactions. A preliminary study comparing the pressure dependence of SOZ produced from ·Cl + methane vs. ozone + ethene has been conducted to determine possible differences in Criegee energetics. A laser ionization/mass spectrometer (LI/MS) has been further characterized to study radicals under atmospheric conditions. The distance required for radical production with respect to the inlet aperture of the mass spectrometer has been estimated. The time-of-flight of the hydroxymethyl radical has been confirmed from previous work. A reinvestigation into the timing of the instrument has been conducted. The implications of these results to the goal of studying CI with the LI/MS are discussed.