Pair association and complexation with water of matrix-isolated pyridine N-oxide: A theoretical study of their manifestations in the IR spectrum

The structure and the IR spectra of three types of pair associates of pyridine N-oxide, as well as of three different complexes of this compound with one or two water molecules, are calculated in terms of the supramolecular approach by the B3LYP/6-311+G(d, p) hybrid density functional method. The experimentally observed IR spectrum of pyridine N-oxide in a low-temperature Ar matrix is theoretically interpreted in detail. The agreement in sign and magnitude between all the calculated and observed frequency shifts of fundamental vibrations shows that the hydrogen-bonded complexes make the main contribution to the formation of complex bands of self-associates.