Experimentally, dehydrogenation leading to D2 desorption and carbon deposition is strongly suppressed by Ge addition to the Ptn. For ethylene-Pt7Ge2, the lowest energy isomer in Fig. has ethylene bound to the GM isomer of Pt7Ge2, but despite nearly a dozen attempts starting with varying initial conditions, we were unable to locate the energy of the transition state for C-H bond activation, ΔE(C-H). The C-H scission pathway appears to involve both H migration on the cluster and restructuring of the cluster framework, i.e., the reaction coordinate appears to be quite complex. We note, however, that the next lowest energy ethylene-Pt7Ge2 isomer in Fig. also has ethylene complexed to the GM of Pt7Ge2, and that isomer has ΔE(C-H) of 2.34 eV, compared to ΔEC2H4 of 1.67 eV, strongly favoring intact ethylene desorption over dehydrogenation. The energetics for the higher energy ethylene-Pt7Ge2 isomers favor intact desorption in some cases and decomposition in others, however, these isomers are high enough in energy that they are unlikely to contribute significantly in the experimental temperature range. Other factors that should tend to promote intact desorption over dehydrogenation include the finding that Pt7Ge2 and Pt7Ge2C2 predominately bind ethylene in a π-mode, which tends to favor desorption over dehydrogenation. In addition, entropic effects tend to favor desorption over decomposition because the transition states for desorption tend to be loose (low frequencies for hindered rotations and cluster-ethylene vibrations), compared to the 3-or 4-centered transition states expected for C-H bond activation (see Figs. ). Another final factor to consider is that the TPD experiments start with the clusters saturated with ethylene, and as explained above, this fact accounts for the observation that the initial desorption is always of intact ethylene, even for Pt7