The nature of the superoxide radical anion in water.

Vibrational properties of the superoxide radical anion (O2(-●) in liquid water have been experimentally investigated for the first time. The stretching frequency, its shift from the gas-phase to aqueous solution, anharmonicity constant, and the Raman bandwidths provide an insight into the radical-water interactions and the hydration cage. In view of the spectroscopic information obtained in this work, the structural models based on molecular dynamics simulation in solution and gas-phase infrared studies of the water molecules bound to O2(-●) are critically examined.