The Pauli principle and the vibrational dynamics of protons in solids: A new spin-related symmetry

Inelastic neutron scattering studies of some hydrogen bonded crystals (e.g. potassium hydrogen carbonate, KHCO3) have revealed that the dynamics Of protons is largely decoupled from the lattice. The KHCO3 crystal is a protolypicaI system for proton dynamics which contains centro-symmetric dimer entities (HCO3-)(2) linked by moderately strong hydrogen bonds, The quantum dynamics of pairs Of coupled oscillators is analyzed. II is shown thai the Pauli principle applied to normal coordinates for fermions gives new quantum properties in the degenerate ground slate. Vibrational wave functions for the singlet ansi triplet slates are derived. A new spin-related selection rule in proposed: the dynamics of fermions (e.g., H atoms) is decoupled from the dynamics of bosuns (e.g., C and O atoms). Scattering functions, for the protons are calculated with various models: the single harmonic oscillator, the double minimum potential and pairs of coupled harmonic oscillators, It is concluded that quantum interferences should be observed with elastic neutron scattering For pairs of coupled fermions, Copyright (C) 1998 Elsevier Science B.V.