Mode-distribution analysis of quasielastic neutron scattering and application to liquid water

Kikuchi, Tatsuya  ; Nakajima, Kenji  ; Kawamura, Seiko   ; Inamura, Yasuhiro  ; Yamamuro, Osamu*; Kofu, Maiko*   ; Kawakita, Yukinobu  ; Suzuya, Kentaro; Nakamura, Mitsutaka   ; Arai, Masatoshi

A quasi-elastic neutron scattering (QENS) experiment is a particular technique that endeavors to define a relationship between time and space for the diffusion dynamics of atoms and molecules. However, in most cases, analyses of QENS data are model dependent. We have developed a new method for processing QENS data without a specific model, wherein all modes can be described as combinations of the relaxations based on the exponential law. By this method, we can obtain a new distribution function, , which we call the mode distribution function (MDF), to represent the number of relaxation modes and distributions of the relaxation times in the modes. The deduction of MDF is based on the maximum entropy method. We report the first application to experimental data of liquid water. In addition to the two known modes, the existence of a new relaxation mode of water molecules with an intermediate time scale has been discovered.