Pressure and Temperature Dependence of the Longitudinal Deuterium Relaxation Times in Supercooled Heavy Water to 300 MPa and 188 K

Abstract

AbstractThe longitudinal deuteron relaxation times T1 in heavy water have been determined at 15.4 MHz in the temperature range from T = 283 K to 188 K and up to pressures of 300 MPa. Between 283 K and 200 K all isotherms exhibit pronounced maxima of T1 in the pressure range between 150 MPa and 300 MPa. This maximum is most pronounced in the 242 K isotherm, where T1 increases more than fourfold from 17 ms at 0.1 MPa to 73 ms at 250 MPa. The 225 MPa isobar runs at 192 K through a minimum: T1 = 0.5 ms. Under the assumption of isotropic reorientation one derives from the minimum condition (ω0 ·τθ ⋍ 0.62) the deuteron quadrupole coupling constant for D2O to CDQC = 214 ± 12 kHz. The isobaric temperature dependence of the correlation times τθ can be described at p ≥ 200 MPa by the VTF‐equation. At p ≤ 100 MPa τθ increases faster with falling temperature than predicted by the VTF‐equation. In this range the isobars are best represented by an equation proposed by Speedy and Angell: The determination of τθ permits an estimate of the viscosity η and the self‐diffusion coefficient D for D2O in the supercooled range. Around T = 190 K and p = 225 MPa one gets η ⋍ 4 Pa · s and D ⋍ 6 · 10−9 cm2/s.