Coupling between molecular rotations and OH•O motions in liquid water:: Theory and experiment

A new theory is proposed to describe spectral effects of the coupling between molecular rotations and OH...O motions in liquid water. The correlation function approach is employed together with a special type of development in which the coupling energy of these two motions is the expansion parameter. The isotropy of the liquid medium plays an essential role in this study. Based on this theory, a new infrared pump-probe experiment is described permitting a visualization of molecular rotations at subpicosecond time scales. Full curves relating the mean squared rotational angle and time, and not only the rotational relaxation time, are measured by this experiment. However, very short times where the incident pulses overlap must be avoided in this analysis. The lifetime of OH...O bonds in water is rotation-limited. (C) 2002 American Institute of Physics.