The static and dynamic surface composition of formamide-benzyl alcohol and water-formamide liquid mixtures studied by means of HeI photoelectron spectroscopy

Abstract

The free surfaces of two binary liquid mixture systems over the whole range of bulk molar composition have been studied using HeI photoelectron spectroscopy in a thin, fast flowing jet arrangement. The spectra of the first group of mixtures, benzyl alcohol and formamide, are found to be deconvolutable by a weighted sum of the pure component spectra. Slight deviations in the procedure allow an estimate to be made of the surface orientation of single benzyl alcohol molecules on top of the formamide solvent. The relative surface composition in the top layer is extracted by the deconvolution procedure. Time relaxation of the surface composition is observed with time constants of the order of several tens of mus. The results of the second group of mixtures, water and formamide, show more complicated features, with one component rapidly evaporating on the time scale of the experiment. The relative surface composition is estimated by a constrained deconvolution involving mainly the first two ionization bands of the components. The location of individual peak structures changes markedly with the mixture composition ratio. The energy values of the first ionization bands indicate a solvent-solvate transition near a 2:1 to 3:1 bulk molar fraction of water. Time relaxation of the surface composition is observed also in these mixtures.