Comment on “Quasielastic neutron scattering of two-dimensional water in a vermiculite clay” [J. Chem. Phys. 113, 2873 (2000)] and “A neutron spin-echo study of confined water” [J. Chem. Phys. 115, 11299 (2001)]

We suggest that in the recent papers [J. Chem. Phys. 113, 2873 (2000)] and [J. Chem. Phys. 115, 11299 (2001)] an incorrect expression was used to obtain the diffusion coefficient of water in fully hydrated vermiculite clay from the Q dependence of the quasielastic neutron scattering data. This has led to underestimating the mean square jump length and the translational diffusion coefficient by a factor of 3. We discuss the correct way to extract the diffusion parameters and their properly estimated values.