Classical trajectories are used to investigate the internal dynamics of the model molecule H–C–C. Two different anharmonic potential energy surfaces which exhibit intrinsic non-RRKM lifetimes are found to contain a large number of quasiperiodic trajectories at energies in excess of H–C–C→H+C=C dissociation threshold. Rotational excitation of H–C–C does not destroy the quasiperiodic motion. The quasiperiodic trajectories are displayed by projections into different coordinate planes and by surfaces of section. The relationship of these results to unimolecular rate theory is briefly discussed.