The effect of protonic motion on the electronic properties of hydrogen-bonded complexes

Electronic population changes and the evolution of the contour maps of the charge density and its Laplacian are used to study the polarizability of hydrogen bonds as a function of the position of the proton within the hydrogen bond. Standard ab initio molecular orbital theory at the 4–31G level (44-31G* for sulphur) has been used to study the complexes between the acceptors, formaldehyde and thioformaldehyde, and the donors, hydrogen fluoride and the ammonium cation. A number of important conclusions for the interpretation of infrared spectra are discussed.