Aids to Analysis of Patterns Obtained in the Diffraction of Electrons by Gases

Abstract

Three techniques have been found particularly useful in the analysis of the electron diffraction patterns produced in the scattering of electrons by gases. The first is the use of a continuously rotating shutter which is placed directly in front of the photographic plate used to record the patterns. The shutter has an angular opening proportional to the third power of the distance from the center of the pattern and serves to reduce greatly the high background intensity gradient which is characteristic of electron scattering. The second is the application of a Fourier computing scheme to the transformation from intensity curves, derived from observed patterns, to the ``radial distribution function'' which is of value in selecting a model for the molecule whose structure is being determined by the analysis. The third technique is the computation of patterns corresponding to various molecular models by means of a graphical synthesizer in (sinx)/x. This synthesizer has advantages over the usual numerical computing schemes in that it takes account of the angular variation of atomic structure factor for electron scattering and also makes evident the contributions of scattering by specific atom pairs to the complete synthesized intensity curve.