Intermolecular vibrations of different isotopologs of the water dimer: Experiments and density functional theory calculations.

Far infrared spectra of seven different isotopologs of the water dimer have been measured in neon matrices at 2.8 K. The experiments are interpreted with the aid of density functional theory calculations, in particular the calculated harmonic isotopic shifts were utilized. All six intermolecular vibrational modes of the water dimer and the fully deuterated water dimer are assigned based the isotopic shifts induced. 31 of a total of 42 intermolecular fundamental modes of the seven different H, D, and (18)O containing water dimers have been experimentally observed and assigned accordingly. The overall agreement between the calculations and the experiments of all isotopologs results in a complete and consistent description of these modes.