PHOTODISSOCIATION OF IBR NEAR 267 NM BY CENTER-STRIPE ANALYSIS OF 2-DIMENSIONAL IMAGE

The photodissociation dynamics of IBr has been investigated near 267 n m by a two-dimensional photofragment imaging technique. Speed and angu lar distributions for Br(P-2(3/2)) and Br(P-2(1/2)) fragments are obta ined from the center-stripe analysis of their images. Using the speed distributions, three dissociation channels are proposed with the forma tions of I(P-2(3/2))+Br(P-2(3/2)), I(P-2(3/2)) +Br(P-2(1/2)), and I(P- 2(1/2))+Br(P-2(3/2)). All three paths, judging from their anisotropy p arameters, have shown the mixed characters of parallel and perpendicul ar transitions with different degrees. Relative quantum yields for the three channels are also determined and resolved into their anisotropi c transition types. With reference to a recent work at 304 nm [Jung, G riffiths, and El-Sayed, J. Chem. Phys. 103, 6999 (1995)], we present t he complete assignment of the photoexcitation of IBr leading to the th ree channels in the uv band region: the perpendicular transition to (1 ) Pi(1)(2341) state predominantly for I(P-2(3/2))+Br(P-2(1/2)), the pa rallel transition to (3) Pi(0)+(2341) mainly for I(P-2(1/2))+Br(P-2(3/ 2)), and the mixed transitions of the parallel to (3) Pi(0+)(2341) and /or to (3) Sigma(0+)(-)(2422) and perpendicular to (3) Pi(1)(2341) sta tes for I(P-2(3/2))+Br(P-2(3/2)) channel, respectively. The nonadiabat ic couplings and the order of vertical energy levels between excited s tates are discussed in terms of difference of the relative quantum yie ld at different excitation photon energies. (C) 1997 American Institut e of Physics.