NMR Study of Water Structure in Super- and Subcritical Conditions

The proton chemical shift of water is measured at temperatures up to $400°\mathrm{C}$ and densities of $0.19$, $0.41$, $0.49$, and $0.60\mathrm{g}/{\mathrm{cm}}^3$. The magnetic susceptibility correction is made in order to express the chemical shift relative to an isolated water molecule in dilute gas. Comparison of the chemical shifts of water in neat fluids at high temperatures to those in organic solvents at ambient conditions shows that the hydrogen bonding persists in supercritical water. At each density, the strength of the hydrogen bonding is found to reach a plateau value at high temperatures.