A Photon Echo Peak Shift Study of Liquid Water

The first photon echo peak shift study of liquid water is presented. Spectral diffusion within the OH stretching absorption band of HDO in D 2 O takes place on many time scales with a slow component on the order of 5−15 ps. This indicates that fluctuations of local structure of the hydrogen bond network in liquid water are relatively long-lived. Vibrational relaxation of the excited state populates a state which is spectroscopically different from the initial ground state. This leads to an strong enhancement of the peak shift and allows spectral diffusion to be measured for delay times beyond the limit determined by the population relaxation time T 1 . The observed signals are discussed with the help of model calculations.