The matrix isolation technique has been combined with infrared spectroscopy and theoretical calculations to explore the reaction of (CH 3 ) 3 In with O 3 over a range of time scales. Upon twin jet deposition (short reaction time), formation of the novel H 3 COIn(CH 3 ) 2 species along with a low yield of CH 2 O was observed. Subsequent UV irradiation greatly increased the yield of H 3 COIn(CH 3 ) 2 while the intensities of the CH 2 O bands were not affected. An extensive set of bands were seen for H 3 COIn(CH 3 ) 2 after irradiation and 18 O spectroscopic data was obtained as well. The identification of this species was supported by theoretical calculations at the B3LYP/lanl2dz and B3LYP/dgdzvp levels of theory. Merged jet deposition (longer reaction times) led to high yield of H 2 CO, CH 3 OH and C 2 H 6 , identifications that were confirmed by 18 O substitution. Mechanistic inferences for the initial steps of this reaction are discussed.