Anomalous Slowing Down of the Vibrational Relaxation of Liquid Water upon Nanoscale Confinement

We study the vibrational dynamics of nanodroplets of liquid water with femtosecond two-color midinfrared pump-probe spectroscopy. For the smallest nanodroplet, containing 10--15 water molecules, the lifetime T₁ of the O-H stretch vibrations is equal to 0.85±0.1 ps, which is more than 3 times as long as in bulk liquid water. We find that the truncation of the hydrogen-bond network of water leads to a dramatic change of the relaxation mechanism.