Photofragmentation dynamics of CH3I at 248 nm

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Abstract
The vibrational distributions of the methyl fragment resulting from the photodissociation of CH3I at 248 nm are obtained by TOF photofragment spectroscopy. Only excitation of the v 2 (umbrella) mode is observed and the distribution peaks strongly at v = 2 for the electronically adiabatic pathway (I 2 P 1/2) but extends up to ν = 8 for the minor (∼ 30 per cent) non-adiabatic pathway (I 2 P 3/2). Angular measurements show that both pathways result from an initial parallel (3 Q 0 ←N) transition followed by a curve crossing to produce the ground state I fragment. The coupling of the curves is vibronic in nature and probably involves the v 6 methyl rocking mode. The lifetime of the photodissociation is found to be ∼ 1 × 10-13 s.