Two distinct regimes of molecular ejection separated by a well-defined threshold fluence are observed in molecular dynamics simulation of pulsed laser irradiation of an organic solid. At fluences above the threshold a collective multilayer ejection or ablation occurs where large liquid droplets are ejected and the total yield of the ablated material follows a critical volume density of the deposited energy. Below threshold thermal desorption from the surface is observed and the desorption yield has an Arrhenius-type dependence on the laser fluence. The yield of monomers does not have a step increase at the threshold and thus deceptively does not give a straightforward interpretation of the ejection mechanisms. © 1999 American Institute of Physics.