Ethylene TPD experiments were done by exposing a sample to 10 L of C2D4 at 150 K, chosen to saturate Pt-associated binding sites, while minimizing adsorption on the alumina support. The sample was then moved to within 0.5 mm of the skimmer cone aperture separating the main UHV chamber from a separately pumped chamber containing a quadrupole mass spectrometer. The sample was heated at 3 K/sec while monitoring masses of interest, including C2D4 + and D2 + , as well as potential adventitious species including CO + and H2O + . Repeated TPD runs, with 150 K ethylene exposures prior to each heat ramp, were done to assess how the cluster samples were changed by the TPD process.