Investigation of the Thermal and Photochemical Reactions of Ozone with 2,3-Dimethyl-2-butene

The matrix isolation technique, combined with infrared spectroscopy and twin jet codeposition, has been used to characterize intermediates formed during the ozonolysis of 2,3-dimethy1-2-butene (DMB). Absorptions of early intermediates in the twin jet experiments grew up to 200% upon annealing to 35 K. A number of these absorptions have been assigned to the elusive Criegee intermediate (CI) and secondary ozonide (SOZ) of DMB, transient species not previously observed for this system. Also observed was the primary ozonide (POZ), in agreement with earlier studies. The wavelength dependence of the photodestruction of these product bands was explored with irradiation from lambda >= 220 to >= 580 nm. Merged jet (flow reactor) experiments generated "late" stable oxidation products of DMB. A recently developed concentric jet method was also utilized to increase yields and monitor the concentration of intermediates and products formed at different times by varying the length of mixing distance (d = 0 to -11 cm) before reaching the cold cell for spectroscopic detection. Identification of intermediates formed during the ozonolysis of DMB was further supported by O-18 and scrambled O-6,O-18 isotopic labeling experiments as well as theoretical density functional calculations at the B3LYP/6-31++G(d,2p) level.