Theory and observation of displacement phenomena in coadsorbed films

Displacement refers to a surprising phenomenon observed in a number of adso rption systems. At low temperatures some relatively inert gases, such as kr ypton (Kr) or methane (CH4), are found to displace molecules from preadsorb ed monolayer films of a more condensable species, such as carbon tetrachlor ide (CCl4), from a graphite substrate. We present a simple thermodynamic mo del to explain displacement and make a prediction applicable to both first- order and continuous displacement processes. We also present measurements o n CH4/CCl4 and Kr/CCl4 coadsorbed films from 77-112 K that verify our predi ction and yield the CCl4 film spreading pressure.