The Bethe surface of liquid water

The Bethe surface of liquid water, which was previously calculated by using a semiempirical model, is compared with recently available data from IXS experiments (inelastic x-ray scattering; Compton scattering of high energy photons) in liquid water. No alarming discrepancy is found for a global view of the Bethe surface, in part because the two sets of data have been constrained by the Bethe sum rule. The shape of the Bethe ridge given by the new data is broader than that obtained through the impulse approximation. The extrapolation to the optical limit (viz., at zero momentum transfer) is shown, and the reliability of these data is discussed in detail.