Classical trajectories were used to study H-C-C→H+C=C dissociation on ten different empirical potential-energy surfaces. The surfaces were modified so that the effect of various surface properties on the unimolecular dynamics could be investigated. Surfaces with early dissociation barriers were found to give intrinsically non-RRKM lifetime distributions, but RRKM translational energy distributions at the exit-channel barrier. The final product translational energy distributions for these surfaces are strongly nonstatistical. This arises from exit-channel coupling, which involves HC-stretch-CC-stretch interactions and not HC-stretch-HCC-bend interactions. Surfaces with late barriers yield intrinsically RRKM lifetime distributions and statistical product translational energy distributions.