Quantum characteristics of the hydrogen bond

Most analyses of hydrogen bond strengths and dynamics (e.g. vibrational spectroscopy and transport) have been considered in terms of (model) potential energy functions defined at the Born–Oppenheimer level of approximation. This paper reports an analysis of the quantum dynamics of hydrogen in the bond that focuses on the quantum ground state of the binding hydrogen in the fields of the other atoms. In view of its mass and size, hydrogen is delocalized in its bond much as is the electron in a covalent bond. It is shown, under certain circumstances, that the compression of the A–B distance, with hydrogen in the A–H–B bond space, yields a flatter effective A–B bond potential due to the reduction of hydrogen density along the direct AB bond line. The quantum behaviour of bonding hydrogen also influences dynamical processes such as vibrational spectroscopy and hydrogen or proton transport.