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Quantum Dynamics of Hydrogen Molecules Inside Cages of Clathrate Hydrates Zlatko Bacic, Department of Chemistry, New York University, New York, NY 10003 Clathrate hydrates with encapsulated hydrogen molecules have received a great deal of attention because of their potential as environmentally friendly, efficient, and safe materials for hydrogen storage. In addition, together with fullerenes such as C 60 and C 70, they provide unique opportunities for investigating novel aspects of the highly quantum dynamics of the coupled translational and rotational motions of one or several H 2 molecules nanoconfined inside their cavities. We have performed fully coupled quantum five-dimensional (5 D) calculations of the translation-rotation (T-R) energy levels of one H 2, HD, and D 2 molecule confined inside the large hexakaidecahedral cage of the structure II clathrate hydrate. Highly converged T-R eigenstates have been obtained for excitation energies beyond the j=2 rotational levels of the guest molecules, in order to allow comparison with the recent Raman spectroscopic measurements. The translationally excited T-R states are assigned with the quantum numbers n and l of the 3 D isotropic harmonic oscillator. The top figure shows the translational components of the three n=1, l=1 states of the caged H 2 , which have one quantum of excitation in the translational modes. Quantum 5 D calculations have also been performed for the T-R eigenstates of H 2 in C 70, on the spectroscopically optimized potential energy surface. The bottom figure displays the 3 D isosurfaces of the reduced probability densities of the T-R states with one to four quanta of excitation in the direction of the long axis of C 70.