ORIGIN OF SPONTANEOUS DESORPTION OBSERVED IN DIRECT STICKING PROBABILITY EXPERIMENTS OF WEAK MOLECULAR ADSORPTION

Using two isotopes of ethane, we have investigated the origin of spont aneous ethane desorption previously observed during direct adsorption probability measurements of molecular ethane adsorption onto a cold Pt (111) surface. We believe the spontaneous desorption may result from a phase transition in the ethane adlayer at coverages near monolayer sa turation which shifts adsorbed ethane to a lower binding energy surfac e site and/or molecular configuration. We also provide conclusive evid ence that desorption from the monolayer does not occur during our meas urements of the coverage-dependent sticking probability.