Quantum Dynamics of Hydrogen Molecules Inside Cages of

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Quantum Dynamics of Hydrogen Molecules Inside Cages of Clathrate Hydrates Zlatko Bacic, Department of

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.