Adsorption of perfluoroalkanes on Pt(111): Thermal desorption and infrared reflection-absorption spectroscopic results

Abstract

First results for the adsorption of perfluorohexane and perfluoroheptane adsorbed at 100 K on Pt(111) are presented. Thermal desorption spectra (TDS) of both perfluoroalkanes are similar and show two distinct desorption peaks due to monolayer species in addition to the expected overlayer peak attributed to multilayer formation. The higher-temperature desorption peaks (α1) exhibit simple first-order desorption kinetics and increase in binding energy with increasing number of CF2 groups (consistent with established desorption models). The second desorption peak (α2) was not expected and is hypothesized to be due to adsorption of the perfluoroalkane in a tilted or puckered configuration in which the interaction with the surface is reduced by at least one CF2 unit from α1. Preliminary infrared reflection-absorption spectroscopy (IRRAS) spectra show a shift in the antisymmetric CF2 stretch for the adsorbed species toward higher wavenumber. © 1994 American Chemical Society.