An expression for an epithermal neutron scattering cross section from a water cluster is derived by using a time-dependent wavepacket approach. Both the translational motion of the center of mass of the cluster and the vibrational modes of a proton in the cluster are taken into account. Incident energy dependence on the neutron proton scattering cross sections calculated for a simplified cluster model agrees with experimental results of neutron scattering from water. Time correlation functions of momentum transfer clearly show that both the translational and vibrational motions significantly contribute to the scattering cross section in the low energy regime. (c) 2007 Elsevier B.V. All rights, reserved.