The matrix isolation infrared spectrum of the water—ammonia complex

Abstract

The infrared spectra, in the 4000-200 cm −1 region, of water and ammonia co-deposited in nitrogen and argon matrices have been recorded. The spectra have been interpreted in terms of a linearly hydrogen-bonded 1:1 molecular complex, consistent with the results of gas phase molecular beam electric resonance and infrared spectroscopic studies. Assignments have been made of most of the fundamental vibrations of the complex, and are in general agreement with those published by N elander et. al. in the same two matrices, as well as in neon and krypton. The wavenumbers measured experimentally have been compared with those calculated in a recent ab initio study, with agreement of the order of 8% for the intramolecular modes of the monomer sub-units and of 16% for the intermolecular modes. The extents to which the water and ammonia monomer spectra are perturbed in the 1:1 complex, and in the linear water and ammonia dimers, have been rationalized on the basis of the relative interaction energies in the three aggregates, and correlated directly with the respective calculated hydrogen bond energies.