Imaging of Disordered Protons and Oxygen Atoms in Molecular Compounds of Pharmaceutical Interest and high-T_c Superconducting Oxides from Neutron and X-Ray Data

摘要

CRystallographic Imaging using Maximum Entropy (CRIME) is used to reconstruct 3D electron and scattering densities from X-Ray and Polarized / Unpolarized Neutron diffraction data. It provides a very significant gain with respect to the widespread conventional Fourier Imaging. The state of the art of CRIME is briefly reviewed and then illustrated by three typical examples of current interest pertaining to each one of the three experimental techniques mentioned above: a Hg-based cuprate [using XR], a ruthenate [using PN] and aspirin [using UN]. The crucial part of a priori modeling to produce adverse non-uniform prior densities is emphasized. New features showing up in CRIME reconstructions are deemed reliable if they survive the negative bias induced by the use of plausible advert non-uniform priors, and untrustworthy otherwise. In spite of this negative stand, three important chemical results are obtained :ⅰ) how much oxygen can reliably be located near mercury using X-rays, ⅱ) the highly asymmetric magnetization of Ruthenium and ⅲ) a direct view in real space of where the protons are located in the carboxylic acid part of the aspirin dimer. Neither of these results can be obtained using a conventional analysis.