Monolayers of Linear Molecules Adsorbed on the Graphite Basal Plane:  Structures and Intermolecular Interactions

Abstract

The monolayer phase diagrams for a number of nonpolar, linear molecules adsorbed on the basal plane of graphite are reviewed. Values for some of the transition temperatures such as the 2D gas-liquid critical points and the melting points of the low-density 2D solids are collected. Upon comparison of these data with each other and with the analogous data for some spherical adsorbate molecules on graphite, it is argued that the ratios of the 2D critical temperatures to the bulk 3D critical temperatures for these linear molecules are essentially independent of molecular shape and quadrupole moment. The melting points are much more sensitive to the details of the molecular size and shape, but two major categories can be discerned: weakly quadrupolar molecules which form 2D lattices with all molecules lying parallel to one another and are often incommensurate, and strongly quadrupolar molecules that form herringbone lattices which are often commensurate with the underlying substrate lattice. When molecular orientation changes greatly upon melting, it is found that melting points are abnormally low compared to the systems where this does not occur.

Impact of Potential Models on Adsorption of Linear Molecules on Carbon Black

“…From these plots, we can estimate the 2D-critical temperatures for ethylene and ethane to be 110 and 125 K, respectively. These values are in good agreement with 109 and 130 K, reported by Steele (1996). The values obtained with the AUA4 model are slightly smaller than those predicted by the UA-TraPPE model.…”

Adsorption of helium on isolated C60and C70anions

“…Of interest are their structures, phase transitions, transition temperatures, and possible existence of structurally ordered phases in a second physisorbed layer. For ethylene, for example, seven different solid phases in the first layer have been reported [5]. The degree of order varies; some are commensurate and orientationally ordered, others are incommensurate and orientationally ordered or disordered.…”

Formation of a One-Dimensional Array of Oxygen in a Microporous Metal-Organic Solid

“…In spite of many ex-perimental and theoretical investigations, the adsorption mechanism and ordering state of adsorbed O 2 molecules that form a specific array in nanochannels are not yet clear (3,4). In the past decade, various novel nanochannel structures constructed with metal-organic frameworks have been produced and studied with regard to their adsorption performance with various gas molecules (5)(6)(7)(8).…”