15min:

ZLATKO BA\V CIC´, FRANCESCO SEBASTIANELLI, MINZHONG XU, YAEL S. ELMATAD AND JULES W. MOSKOWITZ, Department of Chemistry, New York University, New York, NY 10003.

The coupled translation-rotation (T-R) eigenstates of a hydrogen molecule inside the small dodecahedral (H₂O)₂₀ cage of the structure II clathrate hydrate have been determined accurately by means of quantum 5D calculations, for para - and ortho -H₂, as well as ortho - and para -D₂. In addition, the ground-state properties of two and three para -H₂ and ortho -D₂ molecules confined in the small cage have been calculated rigorously using the diffusion Monte Carlo method^b. These calculations have provided a comprehensive picture of the quantum T-R dynamics of the encapsulated molecules. The translational modes exhibit negative anharmonicity; j is a good rotational quantum number, with the threefold degeneracy of the j=1 level lifted completely. When two hydrogen molecules are confined, they are effectively excluded from the central region of the cage, and reside within a shell less than 2 bohrs wide. If time permits, the quantum dynamics results for multiple H₂/D₂ molecules inside the large (H₂O)₂₈ cage will be presented.