Isochoric temperature differential of the x-ray structure factor and structural rearrangements in low-temperature heavy water

X-ray structure factors for heavy water were measured at temperatures of 40. 0, 23. 5, 15. 5, 11. 2, 7. 1, 0. 2, and -11. 0^. From these data isochoric temperature differentials (ITD) were constructed for pairs of temperatures =40. 0- (-11. 0) =51. 0, 23. 5-0. 2=23. 3, and 15. 5-7. 1=8. 4 ^ around the maximum density point at 11. 2^. We show that the temperature dependence of the structural parameters can be obtained much more precisely from ITD than from the direct determination of the structure factor. A major structural rearrangement at the second-neighbor shell is identified from the interpretation of the ITD. We then interpret this rearrangement in terms of a possible increased molecular angular correlation of the tetrahedral structure at low temperatures.