On the orientational relaxation of HDO in liquid water.

We use femtosecond mid-infrared pump-probe spectroscopy to study the orientational relaxation of HDO molecules dissolved in H2O. In order to obtain a reliable anisotropy decay we model the effects of heating and correct for these effects. We have measured the reorientation time constant of the OD vibration from 2430 to 2600 cm(-1), and observe a value of 2.5 ps that shows no variation over this frequency interval. Our results are discussed in the context of previous experiments that have been performed on the complementary system of HDO dissolved in D2O.