Deep inelastic neutron scattering on liquid hydrogen in the crossover region between the molecular and atomic regimes

We have measured the double differential cross section of liquid hydrogen using deep inelastic neutron scattering in an intermediate region of momentum and energy transfer where the crossover between the molecular and atomic regimes is expected. The range of the momentum transfer, computed on the basis of the atomic recoil, is between 24.6 and 36.2 Å-1, i.e., beyond the limit where intermolecular interactions are effective and therefore the incoherent scattering approximation applies. The data cannot be reproduced either using a molecular or an atomic model. We find that a satisfactory fit to the data is obtained by a linear combination of the two models. The relative weight of the molecular model turns out a decreasing function of the energy transfer.