The reaction CH 3 CHI + O 2 has been commonly employed in laboratories to produce a methyl-substituted Criegee intermediate CH 3 CHOO, but the detailed dynamics of this reaction remain unexplored. We carried out this reaction by irradiating a flowing mixture of CH 3 CHI 2 (∼70 mTorr) and O 2 (∼4 and 8 Torr) at 308 or 248 nm and observed infrared emission of the products with a step-scan Fourier-transform spectrometer. Upon irradiation at 248 nm with O 2 ∼4 Torr, a Boltzmann distribution of CO (v ≤ 4, J ≤ 25) with average vibrational energy (12 ± 2) kJ mol −1 and of OH (v = 1, J ≤ 5.5) were observed and assigned to be produced from the decomposition of CH 3 C(O)OH* to form CO + CH 3 OH and OH + CH 3 CO, respectively. The observed broadband emission of CO 2 was simulated with two vibrational distributions of average energies (42 ± 3) and (114 ± 6) kJ mol −1 and assigned to be produced from the decomposition of CH 3 C(O)OH* and (methyl dioxirane)*, respectively. The results upon irradiation of the sample at 308 nm are similar, likely indicating a small fraction of energy partition into these products and rapid thermalization of CH 3 CHI*. Compared with reaction CH 2 I + O 2 , the title reaction yielded products with much less internal excitation, consistent with the expectation that these observed products receive much less fraction of available energy upon fragmentation when an additional methyl moiety was present in the parent. The large-v component of CO observed in experiments of CH 2 I + O 2 at 248 nm, produced from secondary reaction HCO + O 2 , was absent in this work because the corresponding secondary reaction CH 3 CO + O 2 in decomposition of CH 3 CHOO* produces α-lactone + OH or H 2 CO + CO + OH.