The use of high-energy (1200 kV) electrons has been shown to be advantageous in the ab initio structure analysis from electron diffraction of organic compounds. Previous studies showed that ab initio analysis of copper perchlorophthalocyanine could be accomplished ; accelerating voltages at or above 1000 kV, but net at 400 kV for crystals which are about 10 nm thick. Copper perbromophthalocyanine could also be analyzed ab initio at 1200 kV, but the presence of severe dynamical scattering precluded such analysis at lower voltages.
A study of copper perchlorophthalocyanine at accelerating voltages from 200 kV to 1200 kV showed that dynamical scattering accounted for the differences among the diffraction patterns which lead the failure of ab initio analysis at the lower voltages. The series of phthalocyanines offers a good model for the study of dynamical scatterin and direct phasing methods, since it consists of relatively radiation-resistant compounds for which high-resolution diffraction patterns can be obtained.