An avenue to the experimental determination of relativistic effects

Quantum crystallography (QCr) has become a mature field for advanced electron-density refinement of molecules. It has been shown that physical effects such as polarization and electron correlation can be extracted from an X-ray diffraction experiment separately from each other by using QCr techniques. The ultimate goal, however, is the extraction of relativistic effects, which is much more challenging from both a theoretical method development and experimental perspective as it involves heavy elements with many electrons in the core. In this proposal, we tackle such challenges with combined X-ray absorption spectroscopy and variable-wavelength X-ray diffraction experiments on molecular mercury- and bismuth-based crystals.