Relativistic Scattering Factors
Our work includes the development of new experimental and theoretical methods for the study of solids by X-ray diffraction, including the use of very high intensity sources and liquid-helium temperature diffraction equipment. When necessary, experiments are performed at the SUNY X3 beamline at the National Synchrotron Light Source at Brookhaven National Laboratory. Two of the diffractometers in Buffalo are equipped with the same software, electronics and computer hardware as our single-crystal synchrotron instruments at NSLS. In this way students and others can be trained, and perform preliminary experiments before going to NSLS.
We use light excitation of diffractometer-mounted crystals, kept at low temperatures, to study the nature of short-lived species. With the rotating anode source and a mechanical light chopper, we can study the geometry of millisecond lifetime excited species. We will use the time structure of the Advanced Photon Source to extend the studies to transient species with shorter lifetimes.
The use of X-ray diffraction in the mapping of electron densities
sheds new light on the chemical bonding in molecules and the properties
of crystalline materials. The electron density directly gives information
on the nature of chemical bonding, which is important for the understanding
of properties of materials. Recently, we have focused our attention on the
derivation of electrostatic properties, such as dipole and quadrupole moments
and the electrostatic potential, directly from the X-ray data. In the future
work we intend to combine time-resolved studies of transient species, with
the analysis of electron density changes upon molecular excitation.