Hydrogen bonding between the water molecule and the hydroxyl radical (H2O⋅HO): The global minimum

Ab initio quantum mechanical self-consistent-field (SCF) and single and double excitation configuration interaction (CISD) methods have been used in a new study of hydrogen bonding between the water molecule and the hydroxyl radical. The basis sets used are double-zeta plus polarization (DZP) and triple-zeta plus double polarization (TZ2P). The two energetically low-lying minima are 2A′ and 2A″ states, with hydrogen bonding occurring between the oxygen atom in the water molecule and the hydrogen atom in the hydroxyl radical; the 2A′ state has a slightly (∼0.3 kcal/mol) lower energy. The comparable planar C2v symmetry structure lies <0.1 kcal/mol higher in energy. The hydrogen bond distance H...O of the 2A′ is ∼1.94 Å, which is close to that of the water dimer. The ground state dissociation energy is 5.6 kcal/mol, which is larger than that of the water dimer. The predicted infrared spectra for these structures are also reported.