Density functional complete study of hydrogen bonding between the water molecule and the hydroxyl radical (H₂O · HO)

The hydrogen bonding complexes formed between the H 2 O and OH radical have been completely investigated for the first time in this study using density functional theory (DFT). A larger basis set 6‐311++G(2 d ,2 p ) has been employed in conjunction with a hybrid density functional method, namely, UB3LYP/6‐311++G(2 d ,2 p ). The two degenerate components of the OH radical 2 Π ground electronic state give rise to independent states upon interaction with the water molecule, with hydrogen bonding occurring between the oxygen atom of H 2 O and the hydrogen atom of the OH radical. Another hydrogen bond occurs between one of the H atoms of H 2 O and the O atom of the OH radical. The extensive calculation reveals that there is still more hydrogen bonding form found first in this investigation, in which two or three hydrogen bonds occur at the same time. The optimized geometry parameter and interaction energy for various isomers at the present level of theory was estimated. The infrared (IR) spectrum frequencies, IR intensities, and vibrational frequency shifts are reported. The estimates of the H 2 O · OH complex's vibrational modes and predicted IR spectra for these structures are also made. It should be noted that a total of 10 stationary points have been confirmed to be genuine minima and transition states on the potential energy hypersurface of the H 2 O · HO system. Among them, four genuine minima were located.