INTERACTION OF DIMETHYL METHYLPHOSPHONATE WITH ALKANETHIOLATE MONOLAYERS STUDIED BY TEMPERATURE-PROGRAMMED DESORPTION AND INFRARED-SPECTROSCOPY

The adsorption of dimethyl methylphosphonate (DMMP) on well-defined or ganic surfaces consisting of self-assembled monolayers (SAMs) of omega -substituted alkanethiolates on gold has been studied. Three different surfaces were examined: one terminated with -OH groups (Au/S-(CH2)(16 )-OH), one with -CH3 (Au/S-(CH2)(15)-CH3), and one mixed surface with approximately equal amounts of -OH and -CH3 terminated thiols. Detaile d information about the nature and strength of the interaction was gat hered by infrared reflection-absorption spectroscopy and temperature-p rogrammed desorption under ultrahigh-vacuum conditions. It is found th at the outermost functional groups of the thiol monolayer have a prono unced impact on the interaction with DMMP at low coverage. The -OH sur face, allowing for hydrogen bonds with the P=O part of the DMMP molecu le, increases the strength of interaction by approximately 3.8 kJ/mol as compared to the -CH3 surface. A preadsorbed layer of D2O leads to s tronger interaction on all surfaces. This is explained by additional h ydrogen bond formation between free O-D at the ice-vacuum interface an d DMMP.