During the first TPD runs on the Ptn/alumina samples, significant H2O + desorption signal was observed due to adsorption of background water during the cluster deposition process, however, the water signals from Ptn/alumina and Pt-free alumina samples were nearly identical, implying that the adventitious water was mostly adsorbed on the alumina support, and thus should not have significantly affected C2D4 adsorption on the clusters. Adventitious CO (PCO ≈ 4 x 10 -11 Torr) is potentially more problematic, because CO binding strongly to Pt. The deposition times were kept short enough to technique, the "as-prepared", "post-TPD", and other ISS experiments were all done on separate sets of samples. To compensate for any day-to-day variation in He + beam intensity, the Pt and Ge ISS intensities were normalized to the sum of the O, Al, Pt and Ge ISS. A series of ISS experiments was done on each sample, providing additional insight into the morphology of the samples. For adsorbate free clusters, the initial Pt ISS signal is large, and decreases slowly over time as Pt is sputtered from the surface by the 1 keV He + beam. If, however, adsorbates (carbon, CO, etc.) are present on top of the clusters, the initial Pt ISS signal is attenuated, but tends to increase during the first few ISS scans as the adsorbates sputter away, then decrease in later scans as Pt begins to sputter. This procedure also allows the "as-deposited" ISS data to be corrected for attenuation from adventitious CO adsorbed during cluster deposition. In essence, the slow decrease in Pt signal observed after sputtering away the CO is extrapolated to the limit of zero He + exposure. For samples that had been heated (during TPD or in the final step of PtGe preparation), the adventitious CO coverages were negligible.