Ab initio molecular orbital calculations of the infrared spectra of hydrogen bonded complexes of water, ammonia, and hydroxylamine. Part 6. The infrared spectrum of the water–ammonia complex

The molecular structure, interaction energy, and infrared spectrum of the linearly hydrogen bonded 1:1 molecular complex of water and ammonia have been predicted by means of a series of ab initio molecular orbital calculations, at the level of second order Møller–Plesset perturbation theory, using the 6-31G** basis set. The calculated wavenumbers and intensities have been compared with those calculated earlier for the respective monomers, and the wavenumber shifts and intensity changes rationalized in terms of the hydrogen bond interaction responsible for the stability of the complex.The calculated hydrogen bond energy of the complex has been compared with those of the linear water and ammonia dimers, reported in a previous publication, and the relative strengths of interaction of the three aggregates have been rationalized on the basis of the electron donor/acceptor capacities of the respective monomer units. Key words: ab initio, infrared spectrum, water, ammonia.