Microscopic dynamics of liquid hydrogen

We have measured the almost-pure incoherent scattering function of liquid parahydrogen using neutron inelastic scattering. The experiment was carried out on TOSCA, a time-of-flight, inverse geometry, crystal analyser spectrometer, operating on the pulsed-neutron source ISIS (UK). Since the instrument kinematic region is close to a line in the (k,E)-plane, we have actually measured the projection of Sinc (k,?) on this line. The measured cross-section gives a direct experimental access to the microscopic dynamic of the centre-of-mass motion of molecular hydrogen. The data have been analysed using the Gaussian approximation and have been compared with the results of a novel Quantum Mechanical Molecular Dynamics simulation technique. The results are encouraging, but claim for further developments of the theoretical approach, as well as for more extensive experimental data.