INELASTIC NEUTRON-SCATTERING FROM LIQUID WATER - THEORY AND SIMULATION

A theory is described to interpret the recent data on incoherent inelastic neutron scattering from liquid water obtained with the help of spallation sources. An analytical theory, similar to those describing optical spectra of liquids, is presented first. The role of the librational motions and of the relaxation of the intramolecular vibrational motions is emphasized. Computer simulation results are discussed next. As fully classical simulations are not appropriate, the quantum degrees of freedom, associated with internal vibrations, are disentangled from the quasiclassical degrees of freedom, corresponding to the rotations and translations. Only the latter are simulated by molecular dynamics. Preliminary simulation results are presented and are compared with experimental data.