Excess Energy and Structural Dependence of the Rate of Energy RedistributionDuring the Photodissociation of Iodotoluenes

摘要

The ortho (2-), meta (3-1), and para (4-) iodotolunes (C7H7I) photodissociated at266 nm and 30.4 nm and were studied with state-selective one-dimensional photo-fragment translational spectroscopy with state-selective velocity, and translational energy distributions are obtained for the ground I(2P3/2) and spin-orbit excited state I*(2P1/2) iodine atoms produced photodissociation. As has been observed in iodobenzene, the ground state I channel observed in each isomer of iodotoluene exhibits both a prompt alkyl iodide-like dissociation channel following a parallel excitation to the alkyl iodide 30(zero)(n, sigma*) repulsive state and curve crossing to the 1Q1(n,sigma*) state, and a slower, indirect dissociation channel following a competitive excitation to aromatic charge transfer (pi, pi*) predissociate excited states at both 266 nm and 304 nm. The I* channel observed at both 266 nm and 304 nm for each isomer results from prompt dissociation resulting from parallel absorption to an alkyl iodide type 3Q(zero)(n, sigma*) state. The rapid I and I* dissociative channels observed for each isomer are found to exhibit strong dependence on the excess excitation. This is discussed in terms of the increase in the density of the vibrational states of the toluene ring. Dissociation times and rates of internal energy redistribution (IER) from the slow dissociative channel (Beta) are estimated for each isomer. For 2-iodotoluene, the rate of IER for the slow I channel increases from 20