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<p>H atoms in strong O–H...O hydrogen bonds having double-well potential energy contours exhibit interesting dynamic behaviour that depends primarily on the shape of the double-well potential. Effective barrier height and asymmetry between the two wells of the potential are two important criteria determining the shape of double-well potential. The Diabatic state model for hydrogen bonds is utilized here to generate the double-well hydrogen bond potential for the O–H...O hydrogen bonds of some of the well-studied hydrogen-bonded crystalline solids, namely potassium dihydrogen phosphate (KDP), tris-potassium hydrogen bisulphate (TKHS) and urea phosphoric acid (UPA). Change in crystal temperature affects the H atom dynamics uniquely in each of these chosen examples, KDP undergoes a structural phase transition at 122&#xa0;K with freezing of H atom disorder in its O–H...O bonds, whereas TKHS having O–H...O bonds very similar to that in KDP exhibits no structural phase transition, and H atom disorder in TKHS continues even at very low temperatures up to 5&#xa0;K, while H atom in O–H...O bonds of UPA exhibits temperature-induced mobile proton behaviour. We attempt here to understand the unique H atom dynamics in each of these crystals on the basis of temperature-induced changes in the shapes of their double-well O–H...O hydrogen bond potentials.</p>

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Hydrogen atom dynamics in double-well hydrogen bond potentials: a case study of O–H...O bonds of potassium dihydrogen phosphate, tris-potassium hydrogen bisulphate and urea–phosphoric acid crystals

  • 期刊论文

  • 发表日期：

    2025年11月10日

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  • Rajul Ranjan Choudhury,
  • R Chitra

摘要

H atoms in strong O–H...O hydrogen bonds having double-well potential energy contours exhibit interesting dynamic behaviour that depends primarily on the shape of the double-well potential. Effective barrier height and asymmetry between the two wells of the potential are two important criteria determining the shape of double-well potential. The Diabatic state model for hydrogen bonds is utilized here to generate the double-well hydrogen bond potential for the O–H...O hydrogen bonds of some of the well-studied hydrogen-bonded crystalline solids, namely potassium dihydrogen phosphate (KDP), tris-potassium hydrogen bisulphate (TKHS) and urea phosphoric acid (UPA). Change in crystal temperature affects the H atom dynamics uniquely in each of these chosen examples, KDP undergoes a structural phase transition at 122 K with freezing of H atom disorder in its O–H...O bonds, whereas TKHS having O–H...O bonds very similar to that in KDP exhibits no structural phase transition, and H atom disorder in TKHS continues even at very low temperatures up to 5 K, while H atom in O–H...O bonds of UPA exhibits temperature-induced mobile proton behaviour. We attempt here to understand the unique H atom dynamics in each of these crystals on the basis of temperature-induced changes in the shapes of their double-well O–H...O hydrogen bond potentials.