Moessbauer spectroscopy at very high pressures

The generation of Very High Pressure (VHP) with Diamond Anvil Cells (DAC) and its applications to Moessbauer Spectroscopy (MS) are described. We emphasize the technical aspects of DACs relevant to VHP-MS such as collimation, generation of hydrostatic pressures, pressure calibration, and development of special cells. Examples are given showing the potential of VHP-MS in studies of molecular polymerization, order disorder phase transitions of molecular crystals, configuration transformations, and magnetic properties. (orig.)