A pump-probe experiment is described to study femtosecond dynamics of hydro
gen bonds in liquid water. The key element of the experimental setup is a l
aser source emitting 150 fs pulses in the 2.5-4.4 pm spectral region, at 10
mu J power level. The OH-stretching band is recorded for different excitat
ion frequencies and different pump-probe delay times. Time-dependent solvat
ochromic shifts are observed and are interpreted with the help of statistic
al mechanics of nonlinear optical processes. Using these spectral data, the
OH...O motions are "photographed" in real time.