VIBRATIONAL AND ORIENTATIONAL RELAXATION OF MONOMERIC WATER-MOLECULES IN LIQUIDS

A polarization resolved infrared double resonance experiment with picosecond pulses has been used to measure the vibrational and orientational relaxation times of monomeric water and heavy water molecules in different organic solvents after excitation of the antisymmetric nu3 vibration. In all investigated systems a fast (but definitely time resolved) equilibration among the OH (OD) stretch vibrations was found, followed by a rather slow decay of this ensemble. Furthermore hints to a medium lived intermediate state, most likely the bending vibration, are reported. The principal relaxation scheme is very similar to that of water vapor. Comparing H2O and D2O in different solvents significant differences were found, which can be understood at least semiquantitatively. The orientational relaxation times of H2O and D2O differ by a factor of 2, which can be explained by the influence of weak hydrogen bonds of different strength for H2O and D2O on the orientational relaxation. Additionally interesting aspects of the transient spectra are discussed.