THz Spectroscopy of LiquidH2OandD2O

Abstract

We have measured and analyzed the dielectric (0.1--2 THz) response of liquid ${\mathrm{H}}_{2}\mathrm{O}$ and ${\mathrm{D}}_{2}\mathrm{O}$ from 270 to 368 K. The response has been modeled using a Debye model with a fast and a slow decay time. By shifting the temperature scale for the slow decay time of ${\mathrm{D}}_{2}\mathrm{O}$ by 7.2 K we find identical behavior for ${\mathrm{D}}_{2}\mathrm{O}$ and ${\mathrm{H}}_{2}\mathrm{O}$. The temperature dependence and isotope shift of the intermolecular structural relaxation characterized by the slow decay time can be modeled with a singular point at 228 K for ${\mathrm{H}}_{2}\mathrm{O}$ and 235 K for ${\mathrm{D}}_{2}\mathrm{O}$.