EXPONENTIAL-ALPHA-6 POTENTIAL PARAMETERS FROM AB-INITIO CALCULATIONS FOR ATOM MOLECULE INTERACTIONS

Intermolecular parameters for the Buckingham exponential-alpha: 6 central potential have been obtained to represent the interaction of H, N, and 0 atoms with most of the molecules occurring in detonation gases, namely N2, CO2, H2O, CO, NO, H-2 and O2. The interaction energies were calculated using the GAUSSIAN 86 and 88 quantum chemistry computer programs and the configurations chosen so that the median averages over the orientations could be calculated. The calculations have been performed at both Hartree-Fock (HF) level and the Moller-Plesset fourth order perturbation theory level (MP4) and the results are presented either in tabular or diagrammatic form. A novel method, describing the interaction of an atom with a homonuclear diatomic or symmetric linear molecule, based on the median average technique (MAT) is presented which follows directly from the MAT's original equation with no further approximation. We have also introduced some simple approximate equations for unsymmetrical linear and polyatomic systems. The exponential-alpha: 6 form has been fitted to median average potentials obtained in this way, and values for the well depth epsilon, the minimum distance R(m) and the repulsive index alpha have been found for the majority of the atom-molecule systems likely to be of importance.