ABSOLUTE DETERMINATION OF SATURATED ETHYLENE COVERAGE ON PT(111)

We have measured directly the absolute surface coverage of ethylene adsorbed to saturation on a clean Pt(111) surface at 100 K. The fully deuterated compound (C2D4) was substituted for C2H4, enabling quantitative measurements to be made of both C and D areal densities via two independent nuclear reactions. For the C atom coverage, we have measured the C-12(d, p)C-13 yield for incident deuterons of 972 keV energy. For the D atom coverage, we have measured the D(He-3, p)He-4 yield for incident He-3 ions of 630 keV energy. Measurements were made in conjunction with LEED (at 300 K), Auger and thermal desorption spectroscopies. For ethylene adsorption at 100 K, the saturation carbon and deuterium coverages are consistent with C2D4 stoichiometry and the observed coverage was 0.23 +/- 0.02 monolayers. The coverage for adsorption at 300 K, assuming C2D3 stoichiometry, was measured to be 0.21 +/- 0.02 monolayers.