H_2 mean kinetic energy in sII clathrate hydrates as a function of cage occupation and temperature

The dynamic behaviour of more than one molecule caged inside a regular structure is a challenging topic in chemical physics, even from the point of view of quantum simulations. For this reason, we aim to study the mean kinetic energy of the H_2 centres-of-mass, _{CM}, in hydrogen clathrate hydrate samples as a function of the H_2 occupation of the large cages present in this structure (varying from N=0 to 4), and at different values of the temperature (in the range 4 K_{CM} is derived from the Doppler broadening of the H_2 rotational lines observed at high values of Q (>5 A^{-1}). In this regime, the Young and Koppel model applies allowing a complete data interpretation and an accurate extraction of the _{CM}. Contributions coming from single H_2 trapped in the small cages will be estimated and removed, while the important issue of the ortho-parahydrogen ratio will be carefully dealt with.