Experimental inelastic neutron scattering spectrum of hydrogen hexagonal clathrate-hydrate compared with rigorous quantum simulations

Milva Celli, Anna Powers, Daniele Colognesi, Minzhong Xu, Zlatko Bacic, Lorenzo Ulivi

Research output: Contribution to journalArticle

Abstract

We have performed high-resolution inelastic neutron scattering (INS) measurements on binary hydrogen clathrate hydrates exhibiting the hexagonal structure (sH). Two samples, differing only in the ortho/para fraction of hydrogen, were prepared using heavy water and methyl tert-butyl ether as the promoter in its perdeuterated form. The INS spectrum of the translation-rotation (TR) excitations of the guest H2 molecule was obtained by subtracting the very weak signal due to the D2O lattice modes. By means of a subtraction procedure, it has been possible to obtain separately the spectra of caged p-H2 and o-H2. sH clathrates are comprised of three distinct types of cages, two of which, differing in shape and size, are each occupied by one H2 molecule only. Both contribute to the measured INS spectrum which is, therefore, rather complex and challenging to assign unambiguously. To assist with the interpretation, the INS spectra are calculated accurately utilizing the quantum methodology which incorporates the coupled five-dimensional TR energy levels and wave functions of the H 2 molecule confined in each type of nanocage. The computed INS spectra are highly realistic and reflect the complexity of the coupled TR dynamics of the guest H2 in the anisotropic confining environment. The simulated INS spectra of p-H2 and o-H2 in the small and medium cages are compared with the experimental data, and are indispensable for their interpretation.

Original languageEnglish (US)
Article number164507
JournalJournal of Chemical Physics
Volume139
Issue number16
DOIs
StatePublished - Oct 28 2013

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Inelastic neutron scattering
clathrates
Hydrates
hydrates
Hydrogen
inelastic scattering
neutron scattering
hydrogen
simulation
Molecules
Deuterium Oxide
molecules
heavy water
Wave functions
subtraction
confining
Electron energy levels
ethers
energy levels
wave functions

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Experimental inelastic neutron scattering spectrum of hydrogen hexagonal clathrate-hydrate compared with rigorous quantum simulations. / Celli, Milva; Powers, Anna; Colognesi, Daniele; Xu, Minzhong; Bacic, Zlatko; Ulivi, Lorenzo.

In: Journal of Chemical Physics, Vol. 139, No. 16, 164507, 28.10.2013.

Research output: Contribution to journalArticle

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