Quantum Molecular Polyhedra and Atomic Populations

The present paper uses the LCAO MO theory formalism. The structure of the first order electronic density function is decomposed in two kinds of quantum polyhedra to discuss the behavior of quantum atomic populations. Among the many aspects one can consider about atomic populations here, the quantum mechanical structure of the density function is taken as the most important characteristic to think about. Apart of the usual one-electron basis set, centered in the molecular atoms, there is also discussed the possibility that the three-dimensional space where the molecular structures are described can be also the site of basis functions centered in points non-coincident with atomic positions.

Kinetic and Potential Energy Partitioning for Antibonding Molecular Orbitals

Expectation values of kinetic and potential energy are calculated for some lower antibonding orbital states of simple diatomic molecules using H2+ and HeH2+ as test cases. Common LCAO-MO theory and a scaling procedure are applied which allow an analysis of atomic orbital interactions in terms of RUEDENBERG'S1 promotion and interference effect at various internuclear distances. Contributions to the total energy at different regions of interatomic separations are discussed in detail. A characteristic increase of the kinetic energy is observed for antibonding linear combinations at distances where chemical bonding occurs.

EPR-Untersuchungen an elektrolytisch erzeugtem SO2

From the triatomic molecule SO2 with 18 valency electrons we generated the mononegative radical ion with the aid of electrolytic techniques. In this way we could vary the radical concentration over a wide range and could also study the influence of counter ions and solvent molecules. The semi-empirical LCAO-MO theory of WALSH was used to calculate the g-factor shift. UV spectroscopic data of SO2 and Hückel-MO-calculations of the spin density distribution of the unpaired electron in the antibonding MO of SO2- resulted in Δgtheor = (3.9 ± 0.6) x 10-3 which agrees rather well with Δgexp = (3.414 ± 0.003) x 10-3. The quoted error of the theoretical value refers to approximations, which have to be introduced in addition to the approximations of the LCAO-MO theory of WALSH. The HMO spin density distribution compares nicely with the distribution calculated from anisotropic hfs constants of SO2- in a KCl single crystal which have been measured recently by SCHNEIDER et al. Higher concentrations of SO2 molecules resulted in another EPR line with Δgexp = 4.6 x 10-3 which we attribute to the solvated radical ion (SO2)xSO2-. From the temperature dependance of the concentration ratio of the radical species in we determined W = - 6.9 kcal mol-1, x = 2, and K(0 °C) = 8.0 x 10-5 mol2 lit-2.