Temperature dependence of isotopic quantum effects in water.

The technique of high energy x-ray diffraction has been used to measure the temperature variation of hydrogen versus deuterium isotopic quantum effects on the structure of water. The magnitude of the effect is found to be inversely proportional to the temperature, varying by a factor of 2.5 over the range 6 to 45 \ifmmode^\circ\else\textdegree\fi{}C. In addition, the ${\mathrm{H}}_{2}^{16}\mathrm{O}$ versus ${\mathrm{H}}_{2}^{18}\mathrm{O}$ effect has been measured at 26 \ifmmode^\circ\else\textdegree\fi{}C and the structural difference shown to be restricted to the nearest neighbor molecular interactions. The results are compared to recent simulations and previously measured isochoric temperature differentials; additionally, implications for $\mathrm{H}/\mathrm{D}$ substitution experiments are considered.