Infrared Spectra and Pressure-Dependent Yields of the Criegee Intermediate Methyl Vinyl Ketone Oxide and Its Iodoperoxy Adduct

Methyl vinyl ketone oxide (MVKO), a key Criegee intermediate from isoprene ozonolysis, is produced in laboratories via ultraviolet photolysis of 1,3-diiodo-but-2-ene [(CH2I)HC═C(CH3)I] in O2. While the 3-iodo-3-peroxylbut-1-ene [C2H3C(CH3)IOO, denoted IMVKO] adduct becomes stabilized at high pressures, the yield of MVKO decreases. We report the definitive infrared spectral identification of IMVKO, with seven observed bands showing excellent agreement with theoretical predictions. This observation also enables a more accurate MVKO spectrum, correcting prior reports that contained significant IMVKO contributions. By simultaneously monitoring IR bands of syn-MVKO and IMVKO, we quantified the pressure dependence of the syn-MVKO yield relative to the total of syn-MVKO and IMVKO, yαrel, to follow 1/yαrel = (1.08 ± 0.11) + (1.08 ± 0.04)×10–18 [M]. Furthermore, incorporating quantum-chemically predicted IR intensities of MVKO and the loss of the precursor upon photolysis, the absolute yield (yα) of MVKO was estimated as 1/yα = (2.74 ± 0.40) + (3.00 ± 0.13) × 10–18 [M]. Possible reasons for MVKO’s smaller yield than CH2OO are discussed.