Temperature Dependence of Hydrogen Bond Nature in K_<b>3</b>H(SO_<b>4</b>)_<b>2</b>

Abstract

Structure analysis of K 3 H(SO 4 ) 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 parameters, 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 behavior explains why K 3 H(SO 4 ) 2 has no phase transition in spite of the existence of the disordered character at room temperature.