Collective excitations in solid hydrogen as observed by incoherent neutron scattering

Bickermann, A.; Spitzer, H.; Stiller, H.; Meyer, Horst; Lechner, R. E.; Volino, F.

doi:10.1007/bf01351543

Cited by 24 publications

(10 citation statements)

References 17 publications

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“…The spectrum of solid hydrogen (Fig. 2a) shows some maxima, which can be assigned to peaks in the phonon density of states and combination lines of phonons and rotational transitions, in perfect agreement with [3]. For H2 in argon (Fig.…”

Section: Methodssupporting

confidence: 71%

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Inelastic neutron scattering of hydrogen trapped in solid argon

Langel

1984

Rev. Phys. Appl. (Paris)

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2014 La diffusion inélastique des neutrons par des molécules d'hydrogène isolées dans une matrice d'argon et par l'hydrogène pur dans la phase solide a été étudiée. Les pics de la rotation libre de l'hydrogène sont mesurés dans les deux échantillons, et aucun décalage de position n'est observé entre les deux spectres. Les spectres de l'hydrogène pur montrent des effets du recul importants pour un transfert de moment élevé (7 Å-1), contrairement aux spectres de l'hydrogène dans la matrice d'argon. Abstract 2014 Molecular hydrogen was isolated in an argon matrix. Its inelastic neutron scattering functions at momentum transfers of 1 to 7 Å-1 were compared with those of solid hydrogen. Both samples show free rotation without line shift. At high momentum transfer (7 Å-1), the spectrum of pure hydrogen is affected by recoil, whereas no recoil effects could be seen in matrix isolated H,.Revue Phys. Appl. 19 (1984) 755-757 SEPTEMBRE 1984, 1. Introduction.

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Section: Methodssupporting

confidence: 71%

“…The neutron scattering of molecular hydrogen was intensively studied until now, both experimentally and theoretically [2]. In solid hydrogen, a maximum in the phonon density of states was found at 5.4 meV [3]. The ortho para-transition in the solid is found at energies of 13.5 to 14.6 meV, whereas the gas phase value is 14.6 meV.…”

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confidence: 99%

Inelastic neutron scattering of hydrogen trapped in solid argon

Langel

1984

Rev. Phys. Appl. (Paris)

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“…25 The high energy edge of the phonons up to mid-100 cm −1 is also similar to the experimental observations of neutron scattering. [12][13][14] The agreement with experiments of the phonon frequency, which is highly sensitive to external pressure, ensures that this simulation realized the vaporpressure solid.…”

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confidence: 81%

“…[1][2][3][4][5] The solid-hydrogen phase diagram is greatly modified by accounting for such nuclear quantum effects (NQEs). [6][7][8][9] This typical quantum solid has actually attracted a number of theoretical and experimental researchers who adopted Raman scattering, 10,11 neutron scattering, [12][13][14] optical Kerr effects, 15 lattice dynamics calculations, 16,17 and path integral molecular dynamics (PIMD) simulations based on ab initio electronic potentials [6][7][8][9]18 or spherical SilveraGoldman (SG) model potentials. 19 Pressure-induced structural changes have been reported by a combination of synchrotron experiments and density functional theory (DFT)-based PIMD calculations.…”

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confidence: 99%

Communication: Dynamical and structural analyses of solid hydrogen under vapor pressure

Hyeon‐Deuk

Ando

2015

The Journal of Chemical Physics

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Nuclear quantum effects play a dominant role in determining the phase diagram of H2. With a recently developed quantum molecular dynamics simulation method, we examine dynamical and structural characters of solid H2 under vapor pressure, demonstrating the difference from liquid and high-pressure solid H2. While stable hexagonal close-packed lattice structures are reproduced with reasonable lattice phonon frequencies, the most stable adjacent configuration exhibits a zigzag structure, in contrast with the T-shape liquid configuration. The periodic angular distributions of H2 molecules indicate that molecules are not a completely free rotor in the vapor-pressure solid reflecting asymmetric potentials from surrounding molecules on adjacent lattice sites. Discrete jumps of librational and H–H vibrational frequencies as well as H–H bond length caused by structural rearrangements under vapor pressure effectively discriminate the liquid and solid phases. The obtained dynamical and structural information of the vapor-pressure H2 solid will be useful in monitoring thermodynamic states of condensed hydrogens.

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“…Presently we cannot answer these important questions: further experimental and simulation work on semiquantum systems will be surely needed to shed more light on this intriguing subject. Finally, just to exclude any possible instrumental reasons for our experimental findings about the GA breakdown, we also performed an additional measurement on solid polycrystalline para-H 2 at T = 13.3͑1͒K, where the GA is better founded and has been experimentally verified [51]. Recorded scattering data had the sharp elastic line removed, were corrected for multiple scattering and self-absorption as in Sec.…”

Section: B Breakdown Of the Gaussian Approximation In Semiquantum LImentioning

confidence: 99%

Microscopic self-dynamics in liquid hydrogen and in its mixtures with deuterium

et al. 2004

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We have measured the dynamic structure factor of liquid parahydrogen, pure and mixed with deuterium, in various thermodynamic conditions using incoherent inelastic neutron scattering. The experiments were carried out on TOSCA-II, a new time-of-flight, inverse-geometry, crystal-analyzer spectrometer. After an accurate data reduction, the high-energy parts of the neutron spectra recorded in backward scattering were studied through the modified Young and Koppel model, from which the mean kinetic energy values for a hydrogen molecule were estimated. In addition the low-energy parts of the neutron spectra recorded in forward scattering were analyzed in the framework of the Gaussian approximation and fitted through a Levesque-Verlet model for the velocity autocorrelation function. Thus various physical quantities are determined and compared with accurate path integral Monte Carlo simulations. Despite the excellent quality of these fits, the velocity autocorrelation functions derived from the forward-scattering data appear totally unable to properly describe the backward-scattering ones. These findings prove an unquestionable breakdown of the Gaussian approximation in semiquantum liquids. The present results appear of great interest and suggest further investigation on the limits of the widely used Gaussian approximation.

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Collective excitations in solid hydrogen as observed by incoherent neutron scattering

Cited by 24 publications

References 17 publications

Inelastic neutron scattering of hydrogen trapped in solid argon

Inelastic neutron scattering of hydrogen trapped in solid argon

Communication: Dynamical and structural analyses of solid hydrogen under vapor pressure

Microscopic self-dynamics in liquid hydrogen and in its mixtures with deuterium

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