Probing the nature of the K-rotor in unimolecular reactions: Scalar and vector correlations in the photodissociation of NCNO

The photodissociation dynamics of thermal NCNO at 520 and 532 nm have been examined using transient frequency modulation Doppler spectroscopy to measure state-selected CN scalar and vector correlations. Previous work has suggested that the global vibrational and rotational distributions may be described using separate statistical ensembles/phase space theory ~SSE/PST!. We find that the correlated vibrational and rotational distributions are well described by SSE at 520 nm if the K-rotor is considered inactive. At both wavelengths studied, the correlation between the velocity and the rotational angular momentum vector of the CN product is found to be described by phase space theory with no restriction of the projection of the rotational angular momentum vectors along the relative velocity axis. This is indicative of approximate K-scrambling at the transition state, and a discussion of these results in light of the evolution of the K-quantum number is provided. © 2002 American Institute of Physics. @DOI: 10.1063/1.1462581#