Institute for Theoretical Atomic, Molecular and Optical Physics between AMO theory and experiment and promoting AMO theory within the general physics community. It has been involved in some capacity in most of the National Research Council target areas, i.e. precision measurements and tests of fundamental laws, ultracold physics, the development and application of ultra-intense, short wavelength light sources, ultra-fast quantum control of atoms, molecules and electrons, nanoscience, and quantum information science. The Institute is sponsored by the National Science Foundation, the Smithsonian Institution, the Center for Astrophysics and Harvard University. The Armstrong Report in 1987 on "The State of Theoretical Atomic, Molecular and Optical Sciences in the United
Atomic form factor increases with the atomic number, formula_11, of the atoms in a sample. As a result X-rays are not very sensitive to light atoms, such as hydrogen and helium, and there is very little contrast between elements adjacent to each other in the periodic table. For X-ray scattering, formula_12 in the above equation is the electron charge density about the nucleus, and the form factor the Fourier transform of this quantity. The assumption of a spherical distribution is usually good enough for X-ray crystallography. In general the X-ray form factor is complex but the imaginary components only become large near an