N,K ROTATIONAL LEVEL POPULATIONS OF CD3 FROM THE 266-NM PHOTOFRAGMENTATION OF VERTICAL-BAR-JKM] STATE-SELECTED CD3I

The photofragmentation of \JKM] = \111] state-selected CD3I was performed at 266 nm. The \NK) rotational energy level distribution of the resulting vibrationless CD3 photofragment was determined using (2 + 1) resonance-enhanced multiphoton ionization. The \NK) distribution showed that the dominant mechanism during the dynamics on the excited (3)Q(0) surface was Delta K = 0 scattering between the initially excited parent CD3I and the CD3 fragment, i.e., no relative orbital motion about the original C-3 axis of the parent, in agreement with previous non-state selected experiments. In addition, smaller but significant amounts of Delta K = +/-3 scattering also occurred. The outline of a model is provided which attributes the effect of nonhelicity conservation and the Delta K = +/-3 propensity to scattering from regions near the conical intersection between the (3)Q(0) and (1)Q(1) surfaces and in particular to the coupling term between these surfaces. It is therefore suggested that the relative population of the CD3 \NK) energy levels for a given N might provide a quantitative measure of the strength of the nonadiabatic coupling between the two surfaces that correlate asymptotically to the P-2(3/2) and P-2(1/2) spin-orbit energy levels of the atomic iodine photofragment. The experimental INK) rotational distributions are also compared to two recent quantum calculations and are found to be in good agreement for the total scattering into all K levels for a given N. Experimental evidence is also provided, although not analyzed, for the first observation of a detailed photofragmentation differential cross section.