The effect of classical and quantum dynamics on vibrational frequency shifts of H{sub 2} in clathrate hydrates
- Department of Mathematics and Computer Science, Free University Berlin, Arnimallee 6, 14195 Berlin (Germany)
- Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel, Switzerland and Chemistry Department, Brown University, Providence, Rhode Island 02912 (United States)
Vibrational frequency shifts of H{sub 2} in clathrate hydrates are important to understand the properties and elucidate details of the clathrate structure. Experimental spectra of H{sub 2} in clathrate hydrates have been measured for different clathrate compositions, temperatures, and pressures. In order to establish reliable relationships between the clathrate structure, dynamics, and observed frequencies, calculations of vibrational frequency shifts in different clathrate environments are required. In this study, a combination of classical molecular dynamics simulations, electronic structure calculations, and quantum dynamical simulation is used to calculate relative vibrational frequencies of H{sub 2} in clathrate hydrates. This approach allows us to assess dynamical effects and simulate the change of vibrational frequencies with temperature and pressure. The frequency distributions of the H{sub 2} vibrations in the different clathrate cage types agree favorably with experiment. Also, the simulations demonstrate that H{sub 2} in the 5{sup 12} cage is more sensitive to the details of the environment and to quantum dynamical effects, in particular when the cage is doubly occupied. We show that for the 5{sup 12} cage quantum effects lead to frequency increases and double occupation is unlikely. This is different for the 5{sup 12}6{sup 4} cages for which higher occupation numbers than one H{sub 2} per cage are likely.
- OSTI ID:
- 22253601
- Journal Information:
- Journal of Chemical Physics, Vol. 140, Issue 2; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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