Journal of Chemical Physics, Vol.103, No.16, 6999-7005, 1995
Photofragment Translational Spectroscopy of IBr at 304 nm - Polarization Dependence and Dissociation Dynamics
The photodissociation dynamics of IBr has been studied at 304 nm by state-selective photofragment translational spectroscopy. Velocity distributions, anisotropy parameters, and relative quantum yields are 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 IBr at this wavelength. Two sharp velocity distributions observed for the I channel suggest the two dissociation pathways that correlate with ground-state iodine formation. Based on the expected translational energy release and the energy separation between the peaks, the two distributions have been assigned to dissociation of IBr to form I(P-2(3/2))+Br(P-2(3/2)) and I(P-2(3/2))+Br*(P-2(1/2)) with the former channel appearing at higher translational energy. The I* distribution shows one strong peak indicating that there is one dominant channel for formation of I* atoms at this wavelength which has been assigned to dissociation of IBr to form I*(P-2(1/2))+Br(P-2(3/2)) with a quantum yield of 0.1. The I* signal formed from the I*(P-2(1/2))+Br*(P-2(1/2)) dissociation channel is observed very weakly. The observed anisotropy parameter indicates that the I+Br* product (beta=-0.7) is formed mainly from the perpendicular (1) Pi(1)(2341)<--X transition while the I*+Br channel (beta=1.8) is formed predominantly from the parallel 3 Pi(0+)(2341)<--X transition followed by curve crossing to the (3) Sigma(0+)(-)(2422) State. The recoil energy dependence of the anisotropy parameter in the I atom produced in the I+Br channel shows a positive beta value above maximum of the peak recoil energy and a negative value below the peak maximum of the recoil energy distribution. These results are interpreted in terms of the presence of more than one path for the formation of I+Br photoproduct with opposite polarization for their absorbing transitions, most likely the (3) Pi(0+)(2341)<--X and the (3) Pi(1)(2341)<--X transitions. The possible excited state dynamics which give the observed results are discussed in terms of the previously proposed potential energy diagrams for IBr and ICl.
Keywords:JET-COOLED IBR;ION-PAIR STATE;FLUORESCENCE EXCITATION;PHOTODISSOCIATION;LASER;PREDISSOCIATION;SPECTRA;POTENTIALS;ABSORPTION;SCATTERING