THE ADSORPTION OF ETHYLENE DIOXIDE (1.4-DIOXANE) ON A SILVER(110) SURFACE

We have studied the interaction of 1.4-dioxane (=ethylene dioxide (CH2 )(4)O-2) with a silver (110) surface between 90 and 750 K by means of low-energy electron diffraction (LEED), temperature-programmed thermal desorption spectroscopy (TPD), high-resolution electron-energy loss s pectroscopy (HREELS), and work function (Delta Phi) measurements. Diox ane adsorbs molecularly with a high initial sticking probability; up t o 600 K there is no indication of dissociation. In TPD, up to 5 differ ent binding states can be distinguished, which are associated with the population of individual dioxane layers. The desorption temperature o f 220 K for the highest-lying state (desorption energy (Eapproximate to 60 kJ/mol) indicates an interaction which (although primarily of ph ysisorptive character) contains non-negligible ''chemical'' contributi ons. Combined LEED, vibrational loss and Delta Phi measurements indica te that the dioxane molecules of the first layer adsorb in their chara cteristic ''chair'' configuration where the oxygen atoms can specifica lly interact with Ag surface atoms. This also leads to a preferential ordering of the adsorbed molecules within the first layer. This ''orie ntational'' effect of the Ag surface structure is increasingly lost as multilayer formation and condensation of dioxane takes place, althoug h an energetic influence of the Ag surface can be seen in TPD up to th e third layer.