Femtosecond Dynamics of Hydrogen Bonds in Liquid Water: A Real Time Study

Abstract

A pump-probe experiment is described to study femtosecond dynamics of hydrogen bonds in liquid water. The key element of the experimental setup is a laser source emitting 150 fs pulses in the 2.5--4.4 \ensuremath{\mu}m spectral region, at a 10 \ensuremath{\mu}J power level. The OH-stretching band is recorded for different excitation frequencies and different pump-probe delay times. Time-dependent solvatochromic shifts are observed and are interpreted with the help of statistical mechanics of nonlinear optical processes. Using these spectral data, the $\mathrm{OH}\ensuremath{\cdots}\mathrm{O}$ motions are ``photographed'' in real time.