Ion Fragment Imaging of the Photodissociation of Methyl Iodide Small Clusters at 266 nm

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Abstract
Photofragment iodine atoms and methyl radicals from the photodissociation of small clusters of methyl iodide at 266 nm were detected, using ion photofragment imaging spectroscopy. Three different components of the I+ image were observed with average laboratory translational energies of the I fragments, <E(I)> = 2, 16, and 25 kcal mol−1 and anisotropy parameters, β = 0, 2.0 ± 0.6, and 2.1 ± 0.5, respectively. Similarly, for CH3+three different components in the CH3+ image correspond to average laboratory translational energies, <E(CH3)> = 5, 25, and 38 kcal mol−1 and β = 0, 2.0 ± 0.2, and 2.2 ± 0.6, respectively. These results suggest the following reaction mechanisms; a) a CH3I chromophore in small clusters is excited to the A band (n,σ*) system of free CH3I, survives intact within the clusters and dissociates, b) dissociation of the CH3I moiety in the small clusters that have two adjacent iodine atoms results in the formation of slow photofragment iodine atoms and fast methyl radicals, and c) dissociation of other types of small clusters results in the formation of fast iodine atoms and slow methyl radicals.