The adsorption of vapours onto a mercury surface.

The literature reports widely varying adsorption isotherms for the adsorption of the members of the R-OH series on mercury, where R = H,CH3,C2H5,C3H7. By following the variation in the height of the sessile drop of mercury this research investigates the adsorption of members of the series R-OD where R = D,CH3,C2H5,C3H 7 . Deuteration of the -OH group produces the following effects: 1. All the surface pressure TT vs vapour pressure p isotherms are (a) displaced-to lower surface pressures indicating a weaker adsorption, (b) less convex or initially concave to the it axis suggesting reduced adsorbent-adsorbate interaction relative to the adsorbate-adsorbate molecule interaction for the R-OD series. 2. Produces films which are more condensed. 3. Lowers the heat of adsorption by 5 k cal mole -1or more. L. Produces more stable reproducible films. The area per molecule determined for the adsorbed monolayer film agrees with the value calculated for a molecule lying flat on the surface. The adsorption behaviour of the R-OD series is dcminated by the increased and stronger intermolecular hydrogen bonding in the deuterated adsorbate as compared to the undeuterated species.