Binary mixture study of CF$_{4}$ and CF$_{3}$Cl on graphite

In a binary mixture adsorption study of CF$_{4}$ and CF$_{3}$Cl on graphite from 60 K to 105 K, both the CF$_{3}$Cl - \textit{$\nu $}$_{4}$ and the CF$_{4}$ - \textit{$\nu $}$_{3}$ frequency shifts are measured using IRAS as the spreading pressure (chemical potential) of CF$_{4}$ is increased. Even though CF$_{3}$Cl has a much lower saturation vapor pressure (SVP) compared to CF$_{4}$ (at 80 K, SVP of CF$_{4}$ is $\sim $ 70 mT and that of CF$_{3}$Cl is $\sim $ 0.1 mT), the CF$_{4}$ either continuously displaces or adsorbs on top of CF$_{3}$Cl depending on the initial coverage of CF$_{3}$Cl on the graphite surface. For temperatures between 70 K and 105 K and lower coverage of CF$_{3}$Cl, where the molecules lie with their C -- Cl axis nearly parallel with the surface, CF$_{4}$ continuously displaces CF$_{3}$Cl from the surface. For saturated monolayer coverage of CF$_{3}$Cl, where the C -- Cl axis of the molecules are tilted relative to the surface, the CF$_{4}$ molecules adsorb on top of the CF$_{3}$Cl -- HOPG template. At 60 K, the displacement of the low-coverage CF$_{3}$Cl is only partial and the orientation of the remaining CF$_{3}$Cl is tilted relative to the surface from a nearly flat position.