TDS, UPS and NEXAFS show that propylene is di-sigma-bonded on bare Pt(
111) and pi-bonded on K-covered Pt(111) at 95 K. The C-C ''double-bond
plane'' of di-sigma C3H6 is parallel to the surface (as it is for C2H
4). In contrast, the bonding geometry of pi-bonded C3H6 is complex, wi
th the C-C axis being not parallel to the surface (at variance with C2
H4), but the three carbon atoms stay in the same plane.