Title: MEAN KINETIC ENERGY AND FINAL STATE EFFECTS IN LIQUID HYDROGENS FROM INELASTIC NEUTRON SCATTERING
Author(s): G.Corradi (Consiglio Nazionale delle Ricerche, Istituto di Fisica Applicata 'Nello Carrara', Via Panciatichi 64, 50127, Florence, Italy; Universit\`a degli Studi di Firenze, Dipartimento di Fisica, Via G. Sansone 1, 50019, Sesto Fiorentino (FI), Italy), D.Colognesi, M.Celli, M.Zoppi (Consiglio Nazionale delle Ricerche, Istituto di Fisica Applicata 'Nello Carrara', Via Panciatichi 64, 50127, Florence, Italy)

We have measured, using the TOSCA spectrometer at ISIS, the neutron scattering spectrum of liquid para-hydrogen ($T=19.3$~K and $n=25.4$~nm$^{-3}$) and liquid ortho-deuterium ($T=21.3$~K and $n=25.2$~nm$^{-3}$). From the high-energy region of the spectrum, namely $40$~meV${}<\hbar\omega<1$~eV, where the \emph{incoherent approximation} for the center-of-mass motion applies, we have been able to extract the translational mean kinetic energy, which, as expected, turns out to be rather different from the classical values. However, significant deviations from the \emph{impulse approximation} have been detected and the inclusion of some correction terms (accounting for the so-called \emph{final state effects}) had to be accomplished in order to accurately describe the experimental spectra. The comparison of the present mean kinetic energy values with the available experimental and simulated data in the literature is quite good and confirms the excellent performances of TOSCA in the spectroscopic analysis of the condensed phases of liquid hydrogens.

Key words: liquid para-hydrogen, liquid ortho-deuterium, mean kinetic energy, final state effects
PACS: 67.90.+z, 61.12.Ex