INFRARED SPECTROSCOPIC AND TEMPERATURE-PROGRAMMED DESORPTION STUDIES OF DIMETHYLPHENYLPHOSPHINE ADSORBED ON THE COINAGE METALS

The adsorption of dimethylphenylphosphine (dmpp) on gold, silver, and copper has been studied with infrared reflection absorption spectrosco py and temperature programmed desorption mass spectroscopy. This study focuses on phosphine layers that have been prepared on the coinage me tals by deposition from the gas phase in ultrahigh vacuum (UHV). Signi ficant shifts in several infrared bands as well as high stability when heated indicate that a thin chemically bound layer of dmpp has been f ormed on the coinage metals. The activation energy of desorption as re vealed by temperature programmed desorption mass spectroscopy shows th at the interaction with gold is significantly stronger than with coppe r and silver. The properties of the UHV-deposited layers are also comp ared with analogous layers prepared by spontaneous adsorption from dil ute toluene solutions. Infrared spectroscopy suggests that the two met hods of preparation lead to chemically bound layers with dissimilar or ientation and coordination geometries. Moreover, preliminary X-ray pho toelectron spectroscopy data suggest that the solution-prepared layer contains a large fraction of oxidized dmpp. It is also found that the chemical interaction between the phosphine ligands and the metal surfa ces is stronger for the solution than for the UHV-deposited layers. Th e solution-deposited layers on all metals and the gas-phase-deposited layers on gold were found to decompose upon desorption, while the gas- phase-deposited dmpp molecules on copper and silver desorbed as intact entities.