The vibrational spectrum of the water trimer: Comparison between anharmonic ab initio calculations and neon matrix infrared data between 11,000 and 90 cm-1

The infrared spectrum of the water trimer trapped in solid neon has been identified. Eighteen groups of absorptions between 1600 and 11,000 cm(-1) were assigned to one-, two-and three-quanta transitions of the intramolecular modes. Because of the near equivalence of the three molecules and their weak interactions most of these modes correspond to quasi degenerate vibrations involving the bending delta, free OH stretching (OHf) and bonded OH stretching (OHb) of the three subunits at 1608, 3725 and 35253473 cm(-1), respectively. In the last case the 52 cm(-1) splitting is due to the coupling between the OHb oscillators. Calculated anharmonic frequencies correctly agree with these observations and allow to propose a new assignment of the intermolecular modes. Finally combinations of intra + intermolecular transitions were identified and assigned on the basis of calculated anharmonicity coefficients. (C) 2010 Elsevier B.V. All rights reserved.