Partially deuterated water dimers: Microwave spectra and structure

Radio frequency and microwave spectra for various isotopically substituted water dimers have been studied by molecular beam electric resonance spectroscopy. Resolved radio frequency hyperfine transitions have provided information about the tunneling–rotational levels of water dimer. The microwave spectra have been analyzed with a rigid rotor model to give the following structural information: R_oo=2.976 Å (+0.000, −0.030 Å), ϑ_d=−51(10)°, ϑ_a=57(10)° and χ_a=6(20)°. The effects of large amplitude vibrational motion have been estimated and the equilibrium geometry should lie within the above limits. The experimental data is also consistent with χ_a and φ_d equal to zero for the equilibrium geometry. The water dimer structure, therefore, has a symmetry plane, a trans configuration, and a linear hydrogen bond within quoted error limits.