Abnormal effect of conjugated molecules on the fluid–solid phase transition of N 2 and CO adsorbed on graphite

Abstract

Adsorption isotherm measurements were carried out for N 2 on the basal plane of graphite held at a temperature 77 K and preplated with n-alkanes or conjugated species such as mono-substituted benzenes, anthracene, 9,10-dimethylanthracene, and phthalocyanine copper. The isotherm step arising from the fluid–solid phase transition has been found to be abnormally depressed by the conjugated species, whereas the n-alkanes have no effect on the phase behavior of N 2. A similar phase transition for CO has also been found to be depressed by preadsorbed phthalocyanine copper. It is suggested that a small amount of these conjugated species dissolved in N 2 and CO locally induce the 3 × 3 commensurate structure of N 2 and CO to increase the molecular density in the fluid phase and, therefore, to depress abnormally the fluid–solid phase transition of N 2 and CO.