Reorientation of HDO in liquid H2O at different temperatures: Comparison of first and second order correlation functions

We study the temperature dependence of the molecular reorientation of HDO molecules in H2O with polarization-resolved femtosecond mid-infrared pump-probe spectroscopy. With this technique we measure the decay time of the second order correlation function of the molecular reorientation. We find that the reorientation time changes from 4.8 ± 0.3 ps at 1 °C to 0.97 ± 0.05 ps at 70 °C. We compare the measurements with literature results of Terahertz time domain spectroscopy, where the Debye reorientation time is measured. From this comparison we obtain the ratio between the Debye reorientation time and the first order single molecule reorientation time.