Electron crystallography is an emerging technique for which the HVEM is extremely useful, if not essential. Use of high voltage minimizes dynamical effects and thus greatly simplifies structure determination. A series of compounds, the halogenated phthalocyanines, is being examined to determine the limitations of the use of electron diffraction to obtain crystal structures. Diffraction patterns were obtained from the chlorine and bromine analogs for voltages ranging from 100 kV to 1200 kV. Analyses of these data show that the variation with voltage is due to dynamical (coherent multiple) scattering. Data have also been obtained from the fluorene and unhalogenated analogs, but the analysis has not been competed. C60 buckministerfullerine, a compound the crystals of which have significant disorder, is being studied to understand the effects of secondary (non-coherent multiple) scattering. Understanding both dynamical and secondary scattering will be necessary for progress in structure analysis. Most organic compounds form crystals with significant bending. This property is exemplified by anthracene, so this compound is being investigated to understand the consequences of this type of irregularity. Furthermore, anthracene will sublime in the vacuum of the microscope, so the data have to be collected from specimens cooled to about -150oC. Since protein crystals must also be cooled, the study of anthracene will be useful when investigations of macromolecules are undertaken.
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