Thick and thin slices of photoproducts: correlated state distributions in ketene dissociation

We have revisited the correlated product distribution of CH$_{2}$ + CO in the photodissociation of ketene at an energy 2350 cm$^{-1}$ above the barrierless singlet dissociation threshold. Using time-sliced ion imaging, we find the speed distribution of state-selected CO fragments to be quite different from previous measurements. For each CO rotational state observed, the deviations of the coincident CH$_{2}$ distribution from a statistical Phase Space Theory can be accurately described with a single parameter in the spirit of a linear surprisal. The distributions are consistent with calculations of exit channel rotational dynamics starting at a variational transition state.