Microcanonical rates for the unimolecular dissociation of the ethyl radical

We report results on the photodissociation dynamics of the ethyl radical, C2H5. A beam of internally cold radicals is generated by supersonic jet flash pyrolysis of ethyl iodide or n-propylnitrite, respectively. Upon excitation into the A 2A13s Rydberg state ethyl dissociates, presumably on the ground-state surface, into ethylene and a hydrogen atom that is detected by time-resolved photoionization. By varying the excitation energy between 264 and 245 nm, microcanonical rates are obtained as a function of excitation energy. The reaction rates are on the order of 107 s−1, several orders of magnitude slower than expected from simple Rice–Ramsperger–Kassel–Marcus calculations.