TEMPERATURE-DEPENDENCE OF HYDROGEN-BOND NATURE IN K3H(SO4)2

Structure analysis of K3H(SO4)2 was performed by X-ray diffraction experiments at various temperatures down to 27 K in order to investigate the hydrogen bond character in connection with the geometrical isotope effect. The hydrogen bond length R(oo) monotonically decreases with decreasing temperature, accompanied by the contraction of lattice paramaters, and it crosses the critical bond length r(c)(H) at about 100 K. Simultaneously, the double site feature of hydrogen atoms changes into the single site state at the center of the hydrogen bond. This behaviour explains why K3H(SO4)2 has no plate transition in spite of the existence of the disordered character at room temperature.