Signatures of multiple time-scale behaviour in the power spectra of water

Power spectra associated with fluctuations in the tagged particle potential and kinetic energies are analysed for bulk SPC/E water for a range of temperatures along the 1.0 g/cm3 isochore. Fluctuations in the tagged particle potential energies give rise to 1/fα noise, indicative of multiple time-scale behaviour, over a temperature-dependent frequency regime. In contrast, the tagged particle centre-of-mass and rotational kinetic energies, which are indicative of the magnitude of local thermal fluctuations, do not show any evidence of 1/fα behaviour.