Photodissociation of IBr near 267 nm by center-stripe analysis of two-dimensional image

Abstract

The photodissociation dynamics of IBr has been investigated near 267 nm by a two-dimensional photofragment imaging technique. Speed and angular distributions for Br(2P3/2) and Br(2P1/2) fragments are obtained from the center-stripe analysis of their images. Using the speed distributions, three dissociation channels are proposed with the formations of I(2P3/2)+Br(2P3/2), I(2P3/2)+Br(2P1/2), and I(2P1/2)+Br(2P3/2). All three paths, judging from their anisotropy parameters, have shown the mixed characters of parallel and perpendicular transitions with different degrees. Relative quantum yields for the three channels are also determined and resolved into their anisotropic transition types. With reference to a recent work at 304 nm [Jung, Griffiths, and El-Sayed, J. Chem. Phys. 103, 6999 (1995)], we present the complete assignment of the photoexcitation of IBr leading to the three channels in the uv band region: the perpendicular transition to Π11(2341) state predominantly for I(2P3/2)+Br(2P1/2), the parallel transition to Π0+3(2341) mainly for I(2P1/2)+Br(2P3/2), and the mixed transitions of the parallel to Π0+3(2341) and/or to Σ0+−3(2422) and perpendicular to Π13(2341) states for I(2P3/2)+Br(2P3/2) channel, respectively. The nonadiabatic couplings and the order of vertical energy levels between excited states are discussed in terms of difference of the relative quantum yield at different excitation photon energies.