Singlet and triplet excited states of the title compounds were investigated experimentally, using electronenergy-loss spectroscopy (EELS), and theoretically, using density functional calculations that include configuration interaction (DFT/SCI). Both the triplet and the singlet spectra are well rationalized by the theory, permitting an assignment of the observed, broad bands and providing strong indication that DFT/SCI is suitable for the description of excited states in molecules containing third-row elements. The low-lying transitions in tetramethylsilane are found to be 4s and 4p Rydberg; the lowest valence states are higher, at 9.8 eV (triplet) and 10.5 eV (singlet). The lowest triplet band in hexamethyldisilane is found to be valence, the upper orbital having π symmetry. The lowest singlet state is 4s, albeit with zero oscillator strength. The lowest observed singlet band is 4p xy Rydberg with substantial π* valence admixture. The calculated density of excited states is high in tris(trimethylsilyl)silane, and Rydberg-valence mixing is prevalent. A high density of states is found also for tetramethoxysilane, the low-lying transitions being all Rydberg originating from the oxygen lone pair orbitals. Excitation functions for selected vibrational and electronically excited states are presented. The former provide the electron attachment energies. The latter indicate large cross sections for triplet excitation near threshold and, thus, imply substantial yield of triplet states under typical plasma conditions. The He I photoelectron spectrum of tetramethoxysilane is also presented.

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The synthesis, structure, and reaction chemistry of dicarbonyl phosphine and carbonyl diphosphine iron complexes with σ-alkyl-π-allyl ligands derived from ring-opened pinene systems are described. X-ray diffraction studies on three representative examples were performed and showed significant differences in the orientation of the phosphine ligands with respect to the σ-alkyl-π-allyl ligands. These differences are caused by steric interactions, as shown by the fluxional behavior of some of the complexes on the NMR time scale. The influence of the phosphine ligand is demonstrated by the reaction of these complexes with CO/AlCl 3 and their photolysis products in acetic acid.

A novel epitaxial growth method for fabricating mesa patterns on a micrometer scale has been investigated. Electrical devices have been prepared employing this technique and their characteristics are in good agreement with those of mesa etched devices.