Electron Spectroscopy Studies of the Surface Composition in the H₂SO₄/H₂O Binary System

The surface composition of the H2SO4/H2O binary system in the temperature range (298−170 K) has been studied using differentially pumped Auger electron and X-ray photoelectron spectrometers designed to perform under equilibrium conditions (PH2O ≈ 10-6−10-4 Torr). Both spectroscopies have been calibrated on pure sulfuric acid solutions to illustrate their ability to provide accurate atomic stoichiometries within the near-surface region. In the case of AES this ability has also been extended as a tool for the study of the surface composition in the H2SO4/H2O binary system under equilibrium conditions. Compositional analysis of this acidified surface indicates that under these experimental conditions the chemical compositions of the bulk and near-surface region are equal within experimental error. Mass spectrometric analysis of the vapor composition indicates equilibration between the acid solution and D2O.