ADSORPTION OF PERFLUOROALKANES ON PT(111) - THERMAL-DESORPTION AND INFRARED REFLECTION-ABSORPTION SPECTROSCOPIC RESULTS

First results for the adsorption of perfluorohexane and perfluorohepta ne adsorbed at 100 K on Pt(111) are presented. Thermal desorption spec tra (TDS) of both perfluoroalkanes are similar and show two distinct d esorption peaks due to monolayer species in addition to the expected o verlayer peak attributed to multilayer formation. The higher-temperatu re desorption peaks (alpha(1)) exhibit simple first-order desorption k inetics and increase in binding energy with increasing number of CF2 g roups (consistent with established desorption models). The second deso rption peak (alpha(2)) was not expected and is hypothesized to be due to adsorption of the perfluoroalkane in a tilted or puckered configura tion in which the interaction with the surface is reduced by at least one CF2 unit from alpha(1). Preliminary infrared reflection-absorption spectroscopy (IRRAS) spectra show a shift in the antisymmetric CF2 st retch for the adsorbed species toward higher wavenumber.