High energy neutron spectroscopy of compressed solid para-hydrogen

The deep inelastic neutron scattering study of solid hydrogen at 12 K at a molar volume of 23.0 cm³by Langel et al. has been extended to 19.5 K para-hydrogen samples compressed to molar volumes of 21.2, 19.5, and 18.3 cm³, respectively. In each case, inelastic scattering peaks were observed at energy transfers a) shifted due to the molecular translational recoil energy plus internal rotational excitation and b) broadened due to the translational motion of the initial single-particle ground state. The data are analyzed directly to yield the average kinetic energy <K E> of the ground state center-of-mass translational motion as a function of molar volume in this quantum solid. Over a 20% decrease in molar volume, <K E> values increase from 76±9 to 141±9 K. These are compared to indirect measurements.