Representative atomic and molecular systems, including various inorganic and organic molecules with covalent and ionic bonds, have been studied by using density functional theory. The calculations were done with the commonly used exchange-correlation functional B3LYP followed by a comprehensive analysis of the calculated highest-occupied and lowest-unoccupied Kohn-Sham orbital (HOMO and LUMO) energies. The basis set dependence of the DFT results shows that the economical 6-31+G* basis set is generally sufficient for calculating the HOMO and LUMO energies (if the calculated LUMO energies are negative) for use in correlating with molecular properties. The directly calculated ionization potential (IP), electron affinity (EA), electronegativity ( ), hardness (η), and first electron excitation energy (τ) are all in good agreement with the available experimental data. A generally applicable linear correlation relationship exists between the calculated HOMO energies and the experimental/calculated IPs. We have also found satisfactory linear correlation relationships between the calculated LUMO energies and experimental/calculated EAs (for the bound anionic states), between the calculated average HOMO/LUMO energies and values, between the calculated HOMO-LUMO energy gaps and η values, and between the calculated HOMO-LUMO energy gaps and experimental/ calculated first excitation energies. By using these linear correlation relationships, the calculated HOMO and LUMO energies can be employed to semiquantitatively estimate ionization potential, electron affinity, electronegativity, hardness, and first excitation energy.

The molecular chemical structure of poly(methyl methacrylate) (PMMA) surface has been studied by sum frequency generation (SFG) vibrational spectroscopy. By using various methods, we have shown that reflected SFG spectra of PMMA collected in our experiments only come from the polymer/air interface, not from the polymer/substrate or the bulk polymer. These SFG spectra are dominated by the vibrational bands from the ester methyl group. Ranges of orientation and orientation distribution of the ester methyl group on the PMMA surface have been deduced. The antisymmetric stretching vibrational band of the alpha methyl group has been detected on the PMMA surface. Analysis shows that the alpha methyl groups are lying down on the surface. The methylene group has not been observed in SFG spectra. For comparison, we have also studied surface chemical structures of poly(methyl acrylate) (PMA) and dimethyl succinate by SFG.

This article presents an exploratory study of a conceptual model of perceived customer value in a business-to-consumer e-commerce setting. Key precursors of perceived customer value included in the model are valence of on-line shopping experience, perceived product quality, perceived risk, and product price. Relationships among these variables (as well as mediating variables) and their relationship to on-line shoppers' value perceptions are explored. The theoretical framework proposed in this work expands on previous efforts on perceived customer value by including new variables relevant to an e-commerce setting and by integrating several key variables into one model. The preliminary findings lead to several implications. ᭧