Infrared absorption of iodomethylperoxy (syn-ICH2OO) radical generated upon photolysis of CH2I2 and O2 in solid para-H2
Irradiation of a para-hydrogen (p-H2) matrix containing diiodomethane (CH2I2) and O2 at 3.2 K with light at 280 ± 20 nm, followed by annealing of the matrix at 4.0 K, yielded infrared (IR) absorption lines at 2982.4, 1408.9, 1231.8, 1226.5/1225.6, 1085.6, 917.7, 841.6/841.1, 550.5, and 490.2 cm-1 that are assigned to the syn-iodomethylperoxy (syn-ICH2OO) radical. Further irradiation of the matrix at 365 nm diminished these features. Experiments with CH2I2 and 18O2 yielded lines of syn-ICH218O18O at 1407.3, 1228.1/1227.7, 1217.7/1217.0, 1031.5, 899.9/899.4, 836.7/836.0, and 473.6 cm-1. The assignments are based on the photolytic behaviour and comparisons of observed vibrational wavenumbers, IR intensities, and 18O-isotopic shifts with those predicted with the B3LYP/aug-cc-pVTZ-pp method. The observation is consistent with a mechanism that, upon photolysis of CH2I2 at 280 nm, CH2I was formed and subsequently reacted with O2 to yield syn-ICH2OO. Compared with the gaseous reaction CH2I + O2 → CH2OO + I at low pressure, observation of ICH2OO in a p-H2 matrix instead of CH2OO in the gaseous phase indicates that the excess energy of internally excited ICH2OO, produced upon reaction of CH2I + O2, was rapidly quenched in the matrix so that ICH2OO became readily stabilised without further decomposition to form CH2OO + I.