Illumination of polyoxotungstates generates a short-lived excited state which decays to form the reactive intermediate wO that is responsible for subsequent transformation of organic substrates. It is shown by laser flash photolysis that wO is formed with a quantum yield of 0.6 and that it survives for ca. 55 ns in deoxygenated acetonitrile. In the presence of a substrate such as propan-2-ol wO reacts to produce the one-electron-reduced species, as characterized by transient spectroscopy and as confirmed by pulse radiolysis. Oxygen intercepts the initially-formed radicals so that this methodology may be used to follow the course of the reaction. Under continuous photolysis, propan-2-ol is converted into acetone and hydrogen peroxide but with adamantane as substrate the corresponding hydroperoxides are formed. Quantum yields of oxygen consumption have been measured for a variety of other substrates and range from ca. 0.05 for pure acetonitrile to ca. 0.5 for propan-2-ol. In the absence of other substrates, reaction of organic counterions may be observed. All these observations are consistent with hydrogen-atom abstraction from an organic substrate by wO, followed by rapid deprotonation of • wOH and/or trapping by O 2 . A concise reaction scheme involving coupling between oxyradicals is proposed that adequately describes the overall chemistry.

Time-resolved I R emission spectroscopy has been used to monitor the fluorescence in the C-H stretch region of methyl radicals produced in the 193-nm photolysis of acetone. Spectra collected at 20-cm-l resolution in the u3 spectral region do not exhibit any structure. This indicates that the emission in this region is due to both the u3 fundamental of CH3 and combination bands of the radical which overlap each other. Modes other than ~~( 0 0 n O ) must contribute to the observed emission in the 3000-3350-cm-l region. Translationally hot methyl radicals are also found to undergo very fast T -V energy-transfer processes via collisions with various noble gases, resulting in enhanced infrared emission. The intensity of the enhanced emission is a factor of 4 or 5 times the emission intensity in the absence of the noble gases, suggesting that most of the radicals are formed in other vibrational states. The results are explained by assuming that the CH3 radical is initially produced in a broad range of vibrational states.