The effect of water temperature and density on stretching vibrations power spectrum of center dot OHaq was studied from ambient to supercritical conditions by molecular dynamics simulation. Decrease in the height, red-shift of the maximum and broadening of the spectrum were found with increasing temperature and decreasing water density. Decomposition of power spectra into Gaussian bands assigned to the radical monomer and hydrogen-bonded complexes center dot OHaq-(H2O)(nHB )(= 1,2,3) showed equal spacing of components and the red-shift relative to the monomer band, linearly increasing with the decreasing number of solvent H-bonds. The radical-water H- bond statistics resulting from band-contribution showed the significant increase in the bond number between 373 and 573 K, associated with breakage of the continuous hydrogen-bond network. At 673 K the degree of hydrogen bonding was significantly controlled by density. We found that the most optimized radical-water complexes were formed when fluid density decreased below the critical value.