Vibrational dynamics in short, strong symmetric hydrogen bonds: General considerations and two examples

The general properties of the special kind of bond known as a short strong hydrogen bond are discussed, with emphasis on those which are symmetric. The focus is placed on the general properties of the motion of the central proton in such XHX bonds and on the interpretation of inelastic neutron spectra observed for the two specific cases of NaH(D3CCOO)2 and the aquonium cation, [H2O–H–OH2]+, of perchloric acid dihydrate. The difficult issue of spectral assignment in this case of high anharmonicity and strong factor group splitting is discussed.