Molecular dimensions for adsorptives

Pore volumes, accessible surface areas, and the thermodynamics of adsorption are essential in the understanding of solid surface characteristics fundamental to catalyst and adsorbent screening and selection. The recently developed Multiple Equilibrium Analysis (MEA) provides a thorough characterization of the adsorption process. Molecular properties such as molecular volumes and projected molecular areas are needed in order to convert moles adsorbed to surface volumes and probe dependent, accessible surface areas. These molecular quantities are also needed in conventional methods for determining areas and pore volumes. Generally, these molecular properties have been estimated from bulk properties, but many assumptions are required. As a result, different literature values are employed for these essential molecular properties. In this article, molecular structures for various conformers of many molecules are calculated using ZINDO. Molecular volumes and excluded molecular areas are determined from these structures and tabulated for a variety of molecules. Molecular dimensions of molecules are another important consideration needed to understand molecular exclusion as well as size and shape selectivity. Molecular dimensions along the symmetry axes are tabulated as well as the two smallest minimum dimensions of each molecule. Examples are presented to illustrate the use of these quantities in shape and size selectivity, molecular exclusion, diffusion, and adsorbent selection.