Quantum dynamics of interstitial H2 in solid C60

Title:
Quantum dynamics of interstitial H2 in solid C60
Authors:
FitzGerald, Stephen; Yildirim, T.; Santodonato, L. J.; Neumann, Daniel A.; Copley, J. R. D.; Rush, Jack J.; Trouw, F.
Abstract:
We present a neutron-scattering study of the quantum dynamics of molecular hydrogen trapped inside solid C60. The loading isotherm is shown to deviate significantly from a standard Langmuir response and follows instead an exponential form, increasing from 40% filling at 130 atm to 90% at 700 atm. Diffraction data confirm that the adsorbed molecules are randomly oriented and sit exclusively at the octahedral site. Inelastic neutron scattering clearly shows the ortho to para conversion of the interstitial hydrogen, which occurs via a transition from the J=1 to J=0 rotational levels. The level scheme shows relatively minor deviations (on the order of a few percent) from the free rotor model with the splitting in the excited level being the same, 0.7 meV, for both H2 and D2. In contrast the shift in the overall level, which is shown to depend critically upon zero-point motion is almost three times greater for H2 than D2. We also identify the translational modes of the trapped molecules which occur at a much higher energy than would be classically predicted and have an isotopic shift on the order of 2.2. Quantum-mechanical model calculations within the self-consistent harmonic approximation indicate that zero-point motion of H2 molecules in the ground state play the central role in understanding the experimental results, and in particular the high energy of the translational modes and the magnitude of their isotopic shift.
Citation:
FitzGerald, S.A., T. Yildirim, L.J. Santodonato, et al. 1999. "Quantum dynamics of interstitial H2 in solid C60." Physical Review B 60(9): 6439-6451.
Publisher:
American Physical Society
DATE ISSUED:
1999-09-01
Department:
Physics and Astronomy
Type:
article
PUBLISHED VERSION:
10.1103/PhysRevB.60.6439
PERMANENT LINK:
http://hdl.handle.net/11282/310329

Full metadata record

DC FieldValue Language
dc.contributor.authorFitzGerald, Stephenen_US
dc.contributor.authorYildirim, T.en_US
dc.contributor.authorSantodonato, L. J.en_US
dc.contributor.authorNeumann, Daniel A.en_US
dc.contributor.authorCopley, J. R. D.en_US
dc.contributor.authorRush, Jack J.en_US
dc.contributor.authorTrouw, F.en_US
dc.date.accessioned2013-12-23T16:30:41Zen
dc.date.available2013-12-23T16:30:41Zen
dc.date.issued1999-09-01en
dc.identifier.citationFitzGerald, S.A., T. Yildirim, L.J. Santodonato, et al. 1999. "Quantum dynamics of interstitial H2 in solid C60." Physical Review B 60(9): 6439-6451.en_US
dc.identifier.issn0163-1829en_US
dc.identifier.urihttp://hdl.handle.net/11282/310329en
dc.description.abstractWe present a neutron-scattering study of the quantum dynamics of molecular hydrogen trapped inside solid C60. The loading isotherm is shown to deviate significantly from a standard Langmuir response and follows instead an exponential form, increasing from 40% filling at 130 atm to 90% at 700 atm. Diffraction data confirm that the adsorbed molecules are randomly oriented and sit exclusively at the octahedral site. Inelastic neutron scattering clearly shows the ortho to para conversion of the interstitial hydrogen, which occurs via a transition from the J=1 to J=0 rotational levels. The level scheme shows relatively minor deviations (on the order of a few percent) from the free rotor model with the splitting in the excited level being the same, 0.7 meV, for both H2 and D2. In contrast the shift in the overall level, which is shown to depend critically upon zero-point motion is almost three times greater for H2 than D2. We also identify the translational modes of the trapped molecules which occur at a much higher energy than would be classically predicted and have an isotopic shift on the order of 2.2. Quantum-mechanical model calculations within the self-consistent harmonic approximation indicate that zero-point motion of H2 molecules in the ground state play the central role in understanding the experimental results, and in particular the high energy of the translational modes and the magnitude of their isotopic shift.en_US
dc.language.isoen_USen_US
dc.publisherAmerican Physical Societyen_US
dc.identifier.doi10.1103/PhysRevB.60.6439en
dc.subject.departmentPhysics and Astronomyen_US
dc.titleQuantum dynamics of interstitial H2 in solid C60en_US
dc.typearticleen_US
dc.identifier.journalPhysical Review Ben_US
dc.subject.keywordFullerenesen_US
dc.subject.keywordInterstitialsen_US
dc.subject.keywordIsotope shiftsen_US
dc.subject.keywordNeutron diffractionen_US
dc.subject.keywordTranslational statesen_US
dc.identifier.volume60en_US
dc.identifier.issue9en_US
dc.identifier.startpage6439en_US
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