Ab initio molecular orbital calculations of the infrared spectra of hydrogen bonded complexes of water, ammonia and hydroxylamine. Part 10. The intermolecular vibrational modes

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The infrared spectra of the stable hydrogen bonded homodimers and heterodimers formed from among water, ammonia and hydroxylamine have been predicted using ab initio molecular orbital theory, at the level of second order Møller-Plesset perturbation theory and using the split valence polarized 6–31G ** basis set. The intermolecular modes may be classified generally as hydrogen bond stretching and in-plane and out-of-plane bending, etc. Depending on the structure and symmetry of the complex, however, the forms of the intermolecular normal modes can vary widely, and we recognize three separate situations: (1) linear hydrogen bonded complexes of C s symmetry, (2) symmetrical cyclic hydrogen bonded complexes with a plane of symmetry (C 2h), and (3) unsymmetrical cyclic hydrogen bonded complexes with no plane of symmetry (C 1). The forms of the normal modes of the complexes within each group are discussed, in the light of their structures, and their computer wavenumbers and intensities.