The effects of dispersive C-n/R-n-attraction on M+/Rg bonding (M+ = atomicmetal ion, Rg = rare gas atom)

It has been shown, using a "model-potential" analysis, that -C-n/R-n disper sive terms can be an important part of the physical bonding in M+/Rg comple xes (M+=atomic metal ion, Rg=rare gas atom) for M+ ions with large, polariz able outer-shell electron clouds. The model potential equation consists of all attractive terms (accurately calculated or estimated) out to 1/R-8, as well as an Ae(-bR) repulsive term. From known D-e, R-e, and omega (e) value s, and the first and second derivatives of the model potential, the repulsi ve constants A and b as well as the effective charge Z of M+ in a particula r M+.Rg electronic state, can be determined. For the typical M+.Rg states c onsidered here, Z=1.02 +/-0.07, indicating that no extra "chemical" effects are necessary to explain M+/Rg bonding. Furthermore, the trends in the der ived Ae(-bR) repulsive curves make good qualitative sense. A term-by-term a nalysis for M+.Rg states where the M+ ion is small and unpolarizable [such as Na+(2p(6)).Rg] shows that -C-n/R-n terms contribute only a few percent t o the bond strengths, while for M+.Rg states where M+ is large and polariza ble [for example, Mg+(3s).Rg], the -CnRn terms can contribute on the order of 40%-50% to the bond strengths, thus rationalizing semiquantitatively sev eral heretofore puzzling D-e, R-e, omega (e) comparative values. (C) 2001 A merican Institute of Physics.