ab initio quantum chemistry methods acid acid dissociation constant benzene chemical formula chemistry dodecahedron enthalpy freezing-point depression hydrochloric acid hydrogen hydrogen bond hydrogen ion hydroxide international union of pure and applied chemistry nomenclature ligand molar mass molecular dynamics nuclear magnetic resonance oxonium ion oxygen ph perchloric acid pi bond point group protonation self-ionization of water solvation strong acid superacid symmetric hydrogen bond thermodynamic free energy water x-ray crystallography