Computer Analysis of X-Ray Diffraction Patterns of Cubic Substances In view of the recent widespread interest in computer applications in chemical education, a computer program has been written t o aid in the teaching of topics related t o X-ray diffraction. Undergraduate students are often introduced to X-ray diffraction in physical or advanced inorganic chemistry courses where the discussion of crystal structures generally includes a treatment of the Bragg equation, discussion of crystal planes and Miller indices, and subsequent indexing of s i m ~ l eoowder diffraction oatterns. These tooies are well suited for comDuter analvsis. Taking the wavelength of the X-ray'radjation and the two-ihets (20) values ior each diffraction line for eubic subctances as input data, theprogram described here (1) determines the d-spacing corresponding to each diffraction line using the Bragg equation, (2) determines the l l d Zvalues for each line, (3)determines the simplest allowed whole number ratio of the lld' values, (4) inderes each line by assigning the Miller indices hkl, ( 5 ) calculates the average unit cell parameter a, and (6) evaluates the extinction conditions and determines whether the lattice is body-centered, face-centered, or primative. The program was written in Fortran IV for use with a Hewlett-Paekard 2100 computer but with the appropriate control cards and minor changes in format statements it is suitable for use with other systems. A listing of the program, instructions for its use, and a sample printout with several examples are available an request. University of S a n t a Clara S a n t a Clara. California 95053
138 / Journal of Chemical Education
Lawrence C. Nathan
