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Neutron and Raman Spectroscopes of 134 and 134a Hydrofluorocarbons Encaged in Na-X Zeolite

  • T. J. Udovic (a1), J. M. Nicol (a1), R. R. Cavanagh (a1), J. J. Rush (a1), M. K. Crawford (a2), C. P. Grey (a2) and D. R. Corbin (a2)...

Abstract

Inelastic neutron scattering methods were used in conjunction with Raman spectroscopy to probe the vibrational density of states of the hydrofluorocarbons (HFCs) 134 (HF2C-CF2H) and 134a (F3C-CFH2) adsorbed in the cages of dehydrated Na-X zeolite. A comparison of the vibrational spectra of the encaged HFC species with those of their gas-phase analogs indicates that the HFCs adsorb nondissociatively at room temperature and are most likely associated with Na cations in the supercages at the SIII sites. Guest-host interactions are manifested by adsorption-induced perturbations of the gas-phase torsional and C-H stretching vibrations and the presence of additional features presumably due to low-energy whole-molecule vibrations and adsorbate-coupled zeolite framework vibrations. Moreover, although the 134 trans conformer is favored by 5 kJ/mole in the gas phase at 300 K, the gauche conformer seems to be more prevalent in the zeolite at this temperature and below. This suggests that a sizeable fraction of the Na-X adsorption sites provides a stabilizing configuration for the otherwise higher-energy gauche conformation, perhaps due to hydrogen-bonding interactions with the zeolite framework.

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References

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1 Corbin, D. R. and Grey, C. P., (DuPont) unpublished data.
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7 Crawford, M. K. and Corbin, D. R., (DuPont) unpublished data.

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