Profiles of hydrogen stretching IR bands of molecules with hydrogen bonds: A stochastic theory. II. Strong hydrogen bonds

Abstract

A theory is proposed to describe the shape of hydrogen stretching IR bands of complexes with strong hydrogen bonds in disordered condensed phases. The theory uses stochastic arguments and represents a generalization of that proposed earlier to study weak and medium-strong hydrogen bonds. The cases of strong asymmetrical and of strong symmetrical or nearly symmetrical bonds are treated separately. The profiles are generated by three essential band shaping mechanisms: the anharmonic coupling between the hydrogen stretching and the bond stretching modes, the Fermi resonance between the singly excited hydrogen stretching and various singly or doubly excited harmonic levels perturbed by hydrogen bonding and the anharmonicity of the hydrogen stretching mode itself. The anomalous isotope effect on the band position and on the integrated intensity is discussed in detail; its existence does not necessarily imply the potential energy surface to have two low energy minima.