Statistical analysis of the recoil energy distributions in the products of the unimolecular dissociations of NO2 and C2O

Recoil energy distributions in the products of the barrierless unimolecular dissociations NO2 → NO+O and C2O → C+CO are derived within the framework of phase space theory (PST) in both cases where the reactant beam is supersonic or thermalized. The strong fluctuations observed experimentally in the distributions are rationalized in terms of vibrational level spacings, angular momentum constraints and the fact that the density of states corresponding to a given rotational energy of the nascent diatomic diverges when this energy tends to zero. Up to now, these fluctuations have not been considered as being compatible with a statistical process.