Where are Protons and Deuterons in KH_pD_{1-p}CO_3? A Neutron Diffraction Study

Abstract

The crystals of potassium hydrogen carbonate (KHCO3) and the KDCO3 analogue are isomorphous. They are composed of hydrogen or deuterium bonded centrosymmetric dimers (HCO3-)(2) or (DCO3-)(2). The space group symmetry of KHpD1-pCO3 (p approximate to 0.75) determined with neutron diffraction is identical to those of KHCO3 and KDCO3. This is at variance with a random distribution of H and D nuclei. These crystals are macroscopic quantum systems in which protons or/and deuterons merge into macroscopic states.