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 e xperiments (inelastic x-ray scattering; Compton scattering of high energy p hotons) 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 const rained 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 sho wn, and the reliability of these data is discussed in detail.