PHOTOFRAGMENT TRANSLATIONAL SPECTROSCOPY OF ICL AT 304 NM

The photodissociation dynamics of ICl is studied at 304 nm by state-se lective photofragment translational spectroscopy. Velocity distributio ns, anisotropy parameters, and relative quantum yields an obtained for the ground I(P-2(3/2)) and spin-orbit excited state I(P-2(1/2)) iodi ne atoms, which are produced from photodissociation of ICl at this wav elength Two sharp velocity distributions are observed for the I channe l, suggesting the existence of two dissociation pathways that correlat e with ground state iodine formation. Based on the expected translatio nal energy release and the energy separation between those peaks, the two distributions are assigned to dissociation of ICl to I(P-2(3/2)) Cl(P-2(3/2)) and to I(P-2(3/2)) + Cl(P-2(1/2)); the former channel a ppears at higher translational energy. The distribution of I also sho ws two strong peaks, indicating that there are two dominant channels f or the formation of I atoms at this wavelength which we assign to the dissociation of ICl forming I(P-2(1/2)) + Cl(P-2(3/2)) and I*(P-2(1/ 2)) + Cl(P-2(1/2)), respectively. The quantum yield of I*(P-2(1/2)) i s determined to be 0.30, indicating that the formation of ground state iodine is clearly the favored dissociation channel at 304 nm. The obs erved anisotropy in the angular distribution of dissociation products (beta) indicates that the I + Cl and I* + Cl* channels are formed pre dominantly from the parallel transition (beta = 1.7 for both channels) while the I + Cl and I + Cl products are formed mainly from perpendi cular transitions (beta = -0.5). The decrease in the anisotropy parame ter of the I formation channels from their limiting value of -1 is att ributed to the presence of more than one path for the formation of I Cl/Cl photoproducts with apposite polarization for their absorbing t ransitions. The possible excited state dynamics, which give the observ ed results, are discussed in terms of the previously proposed energy c orrelation diagram for ICl.