title: The HD molecule in small and medium cages of clathrate hydrates: quantum dynamics studied by neutron scattering measurements and computation.
abstract: We report inelastic neutron scattering (INS) measurements on molecular hydrogen deuteride (HD) trapped in binary cubic (sII) and hexagonal (sH) clathrate hydrates, performed at low temperature using two different neutron spectrometers in order to probe both energy and momentum transfer. The INS spectra of binary clathrate samples exhibit a rich structure containing sharp bands arising from both the rotational transitions and the rattling modes of the guest molecule. For the clathrates with sII structure, there is a very good agreement with the rigorous fully quantum simulations which account for the subtle effects of the anisotropy, angular and radial, of the host cage on the HD microscopic dynamics. The sH clathrate sample presents a much greater challenge, due to the uncertainties regarding the crystal structure, which is known only for similar crystals with different promoter, but nor for HD (or H2) plus methyl tert-butyl ether (MTBE-d12).
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy.
authors.forename: Daniele
authors.initials: D
authors.lastname: Colognesi
authors.affiliation: Department of Chemistry, New York University, New York, New York 10003, USA.
authors.forename: Anna
authors.initials: A
authors.lastname: Powers
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy.
authors.forename: Milva
authors.initials: M
authors.lastname: Celli
authors.affiliation: Department of Chemistry, New York University, New York, New York 10003, USA.
authors.forename: Minzhong
authors.initials: M
authors.lastname: Xu
authors.affiliation: Department of Chemistry, New York University, New York, New York 10003, USA.
authors.forename: Zlatko
authors.initials: Z
authors.lastname: Bačić
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Ulivi