Classical molecular dynamics simulations have been used to investigate the effect of rotational energy and surface temperature on the trapping probability of ethane on Si(100)-2×1. At all translational energies studied, the trapping probability remains constant as the rotational state of the incident molecule is increased to the equivalent of J=20, then decreases as the rotational energy is further increased. Over the range of incident translational energies (0.1–0.6 eV) and angles (0° to 60°) studied, when J=40, the trapping probability has decreased by about 30% relative to the probability at low J values. Computed trajectories also indicate that surface temperature can affect trapping probabilities. Simulations indicate that for trajectories with 0.3 eV of translational energy at normal incidence, increasing the surface temperature from 65 to 200 K will not significantly change the trapping probability. However, if the surface temperature is raised to 600 K, the trapping probability falls to about half of the trapping probability at 65 K. © 2001 American Vacuum Society.