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The adsorption of dimethyl methylphosphonate (DMMP) on well-defined organic surfaces consisting of self-assembled monolayers (SAMs) of ω-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. Detailed information about the nature and strength of the interaction was gathered by infrared reflection−absorption spectroscopy and temperature-programmed desorption under ultrahigh-vacuum conditions. It is found that the outermost functional groups of the thiol monolayer have a pronounced impact on the interaction with DMMP at low coverage. The −OH surface, allowing for hydrogen bonds with the PO part of the DMMP molecule, increases the strength of interaction by approximately 3.8 kJ/mol as compared to the −CH3 surface. A preadsorbed layer of D2O leads to stronger interaction on all surfaces. This is explained by additional hydrogen bond formation between free O−D at the ice−vacuum interface and DMMP.

The adsorption of dimethyl methylphosphonate (DMMP), a model molecule for sarin, on three different organic interfaces, prepared by solution self-assembly of alkanethiols on gold, was followed by a surface acoustic wave mass sensor and infrared reflection-absorption spectroscopy at room temperature. The surfaces, characterized by the following tail groups (-OH, -CH 3 , -COOH), show both quantitative and qualitative differences concerning the interaction with DMMP, the acid surface giving rise to the strongest adsorption. Results obtained in UHV, at low temperatures using infrared spectroscopy and temperature-programmed desorption, support this observation and give complementary information about the nature of the interaction. The hydrogen-bond-accepting properties of the PdO part of DMMP and its impact on the design of sensing interfaces based on hydrogen bonding, as well as the use of self-assembled monolayers to study molecular interactions, are discussed.

Humidity influences the adsorption of dimethyl methylphosphonate (DMMP) on three different organic model interfaces to quite different extents. The model interfaces, characterized by the following tail groups (−OH, −CH3, −COOH), were prepared by solution self-assembly of ω-substituted alkanethiols on gold, and the coadsorption of water and DMMP was followed by a surface acoustic wave sensor and infrared reflection absorption spectroscopy. The surfaces show both quantitative and qualitative differences concerning the interaction with DMMP. Humidity is found to influence the hydrogen bonds formed between DMMP and the tail groups, increasing the strength of interaction. However, the changes in surface coverage of DMMP, as measured by infrared absorption, are not fully registered by the surface acoustic wave sensor, because of a concomitant desorption of water. Indeed there is even a loss in sensor signal due to the presence of humidity in the case of the −COOH-terminated surface, where the strongest interaction with DMMP is found. After compensation for the loss of water, the coverage of DMMP increases with the relative humidity on the OH surface and decreases with the relative humidity on the COOH surface. The consequences of the results are discussed in terms of their impact on the design of sensing interfaces based on hydrogen bonding.