The gas-liquid phase transition shift at surfaces: experimental method and interpretation

Abstract

The shift of the binding energy of a molecule when brought from the gas to the liquid phase has been observed by ESCA and found to carry information on the bulk structure of the investigated liquid. In this paper we report phase transition shifts found by metastable impact electron spectroscopy and UPS for molecules close to the surface of a liquid. We investigate the binary mixture of formamide and benzylalcohol in the whole range of molar ratios from pure formamide to pure benzylalcohol and a novel method is described for the determination of the phase transition shift that overcomes previous problems. Further, we attempt to derive information on the surface structure by interpreting our data within the frame of a model. As an interesting result we find that isolated benzylalcohol molecules have low binding energy to a formamide surface and that they seem to sit on top of an otherwise intact formamide surface layer.