Physical Adsorption on Hexagonal Graphitic Boron Nitride a-BN

6 Physical Adsorption on Hexagonal Graphitic Boron Nitride (a-BN) 

Quantum mechanical investigation at the HF/6-31G (d,p) level leads to a total energy of -81.7513 hartree and a zero-point vibrational energy of 4.5 kcal/mol for a molecule HeBN (Coov symmetry, state). Vibrational frequencies calculated are 1903 (a), 787 (o), and 214 (ji) values in cm symmetries parenthesized. The optimized geometry at the HF/6-31G (d,p) level including partial atomic charges and band population data (from a Mullikan population analysis) is presented in Fig. 4-20 [49]. 

The geometry of HeBN has also been optimized using full-valence CASSCF wave functions with a 6-31G (d,p) basis set. The optimization was stopped at a B-He distance of 3.05 A and at a B-N distance of 1.292 A. This leads to the assumption that He is bound to B-N by dipole-induced dipole forces. The equilibrium distances for ArBN have been calculated at the MP3/6-31G (d,p) level to be r(ArB)=1.847 A and r(BN) =1.250 A [62]. 

Physical adsorption Isotherms of Ar and N2 on a-BN have been determined and analyzed. The adsorption energies distribution functions were calculated using a double Gaussian as distribution function. The Isosteric heats of adsorption were calculated employing the Clausius-Clapeyron equation. Both systems display a sharp maximum upon completion of a statistical monolayer (see Fig. 4-21). For additional Information, see [50]. 

While a monomolecular film of krypton on graphite has an incipient triple point and a commensurate-incommensurate 2D solid transition, this phenomenon does not appear on a-BN. The differences in the Kr-film properties probably originate in the particular size of the Kr atom with respect to the distances of potential wells on the substrate. For relevant compilation of thermodynamic data and diagrams of the adsorption isotherms, see [51 ]. Long-range interactions between rare gas atoms on the surface of a-BN (in context with other 

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