Douglas Dorset is jointly supported by a grant from the Theoretical and Computational Chemistry Program in the Chemistry Division and the Polymers Program in Division of Materials Research to continue his studies of direct methods for electron crystallography. The overall thrust of the research program is to continue the application of direct phasing methods to electron crystallography. Specific goals of the current project are: 1) to improve methods for collecting more accurate electron diffraction intensity data; 2) to optimize the use of direct methods for handling undersampled reciprocal lattices; and 3) to develop refinement procedures which circumvent the difficulties associated with multiple scattering problems. Although the proposal is primarily focused on methodology development, various applications are also proposed on small organic systems such as triphenylene, TCNQ, pyrene, quaterrylene and anthanthrene, and polymeric systems such as whisker crystals of p-oxybenzoate, spider drag line silk, and oriented films of poly(tetrafluoroethylene). X-ray diffraction has had a tremendous impact on the fields of Chemistry and Material Science. It provides a direct experimental probe of molecular structure at the atomistic level. However, for many important organic compounds, only small crystals can be grown that are unsuitable for investigation by X-ray diffraction. Electron crystallography presents a powerful alternative for studying such compounds providing that a number of technical difficulties can be overcome. Dorset's work in this area is directed at improving this alternative to conventional X-ray crystallography to the point where it is precise and relatively easy to use.
