Quasi-Elastic and Inelastic Neutron Scattering and Molecular Dynamics of Water at Supercooled Temperature

Abstract

Recent results of incoherent neutron scattering investigations of water (H2O) at various temperatures, ranging from above the room temperature down to −20°C, are summarized. Analysis of these results in terms of various models are discussed and compared with the available computer molecular dynamics (CMD) simulations in the literature. For the quasi-elastic scattering (QENS) region, the self dynamic structure factor has been analysed in terms of a convolution of translation and rotation of individual water molecules. The translational and the rotational parts were modeled respectively by a jump diffusion and rotational diffusion. Comparisons are then made with recent CMD results to assess the validity of the model description. For the inelastic scattering (INS) region, the analysis focused mainly on the intramolecular vibrations in the liquid state. A satelite peak which appeared beyond the stretch vibrational band was analysed in terms of a quantum mechanical process of exciting the stretch vibrational mode with a simultaneous breaking of the hydrogen bond. The absolute cross section in the stretch vibrational region was compared quantitatively with a CMD result as a function of temperature from 80°C down to −15°C.