Photofragment translational spectroscopy of ICL at 304 nm

The photodissociation dynamics of ICl is studied at 304 nm by state-selective photofragment translational spectroscopy. Velocity distributions, 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)) iodine atoms, which are produced from photodissociation of ICl at this wavelength Two sharp velocity distributions are observed for the I channel, suggesting the existence of two dissociation pathways that correlate with ground state iodine formation. Based on the expected translational 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 appears at higher translational energy. The distribution of I* also shows two strong peaks, indicating that there are two dominant channels for 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)) is determined to be 0.30, indicating that the formation of ground state iodine is clearly the favored dissociation channel at 304 nm. The observed anisotropy in the angular distribution of dissociation products (beta) indicates that the I* + Cl and I* + Cl* channels are formed predominantly from the parallel transition (beta = 1.7 for both channels) while the I + Cl and I + Cl* products are formed mainly from perpendicular transitions (beta = -0.5). The decrease in the anisotropy parameter of the I formation channels from their limiting value of -1 is attributed to the presence of more than one path for the formation of I + Cl/Cl* photoproducts with apposite polarization for their absorbing transitions. The possible excited state dynamics, which give the observed results, are discussed in terms of the previously proposed energy correlation diagram for ICl.