Photofragment orientation as a probe of near-threshold nonadiabatic phenomena in the photodissociation of iodine cyanide (ICN).
Cyanogen iodide (ICN) is photodissociated at 249 nm. The CN(X2S+, n = 2) fragments are probed by sub-Doppler laser-induced fluorescence (LIF) using circularly polarized light, which allows resoln. of the F1 (J = N + 1/2) and F2 (J = N - 1/2) spin-rotation doublets. These components are shown to be oriented, i.e. to possess a non-statistical non-centrosym. MJ quantum-state distribution. The sign and magnitude of the orientation vary between components and are shown to have some correlation with the energetic threshold for prodn. of the I(2P1/2) spin-orbit state. These observations are briefly discussed in the context of breakdown of the Born-Oppenheimer approxn. in this system.
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