Final state effects in the neutron Compton scattering on hydrogen molecules—a new approach

Compton scattering on hydrogen molecules (H2, D2) with neutrons in the 10–100 eV range has recently been discussed in connection with observations of certain unexplained shifts of the Compton peaks at higher scattering angles (possibly indicating a quantum entanglement effect on the sub-fs-time scale). It is therefore worthwhile to look somewhat deeper into the details of the scattering process for these particular systems. One main aspect is the specific situation valid for two-atomic molecules where the vibrational momenta lie only along the molecular axes, another concerns the validity of the impulse approximation and a third main aspect is related to the anomalous cross-sections in the H/D intensity ratios observed for mixed H2/D2 samples. alternative treatment of the so-called final state (FSE) effects the concept of scattering time is analyzed and the elastic slowing-down of the recoiling protons during this time is explicitly calculated and compared, first with those expected from standard FSE calculations and then with experimental data for one specifically chosen, well-studied system, the D2 molecule. The results of the present FSE calculations differ from the standard ones in the high energy tail of the Compton peak, but agrees very well with experiment. Taking into account the line shape differences discussed here should also be of importance for the closer analysis of proton momentum distributions as well as for the interpretation of the H- and D- intensity anomalies.