Raman Spectrum of Solid Orthodeuterium to 150 kbar at 5 K

Wijngaarden, Rinke J.; Silvera, Isaac F.

doi:10.1103/physrevlett.44.456

Cited by 23 publications

(3 citation statements)

References 13 publications

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“…Its crossing and hybridization with the rotons has been described elsewhere. 10 The general behavior is similar for H 2 and D 2 . However, in D 2 at about 150 kbar, the rotons begin to broaden and turn down in frequency.…”

Section: New Low-temperature Phase Of Molecular Deuterium At Ultrahigmentioning

confidence: 79%

New Low-Temperature Phase of Molecular Deuterium at Ultrahigh Pressure

1981

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Section: New Low-temperature Phase Of Molecular Deuterium At Ultrahigmentioning

confidence: 79%

New Low-Temperature Phase of Molecular Deuterium at Ultrahigh Pressure

1981

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“…The intrinsic Raman cross-section of the phonon is very small so that its intensity is primarily due to hybridization with the rotational transitions and the total Raman cross-section is conserved (16)(17)(18); thus we assigned the phonon intensity to the nearest rotational line. Neglect of the phonon intensity has a negligible effect on the calculated rates.…”

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confidence: 99%

Pressure-enhanced ortho-para conversion in solid hydrogen up to 58 GPa

Eggert

Karmon

Hemley

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

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We measured the ortho-para conversion rate in solid hydrogen by using Raman scattering in a diamond-anvil cell, extending previous measurements by a factor of 60 in pressure. We confirm previous experiments that suggested a decrease in the conversion rate above about 0.5 GPa. We observe a distinct minimum at 3 GPa followed by a drastic increase in the conversion rate to our maximum pressure of 58 GPa. This pressure enhancement of conversion is not predicted by previous theoretical treatments and must be due to a new conversion pathway.high-pressure physics ͉ Raman spectroscopy ͉ solid hydrogen S olid hydrogen is a highly compressible quantum molecular solid whose behavior changes drastically over experimentally accessible pressures. Recently, a great deal of attention has been paid to the orientational ordering behavior of solid hydrogen at very high pressures (1-6). Driving this interest is the interpretation of several high-pressure phase transitions as involving orientational ordering, as well as the realization that the insulator-to-metal transition in solid hydrogen depends critically on the orientational properties of high-pressure hydrogen. Crucial to understanding these phenomena is a detailed knowledge of the ortho-para state of the solid at high pressures.The molecular wavefunction for any isolated homonuclear diatomic molecule must be symmetric or antisymmetric under nuclear exchange. For hydrogen the molecular wavefunction must be antisymmetric under proton exchange, which leads to two distinct types of hydrogen: ortho with total nuclear spin I ϭ 1 and para with I ϭ 0. If we restrict ourselves to ground electronic states, the total protonic wavefunction must be antisymmetric and can be written as a product of vibrational, spin, and rotational parts, mol ϭ vib spin rot . vib is always symmetric, and spin is symmetric for the triplet state I ϭ 1 and antisymmetric for the singlet state I ϭ 0. Thus rot must be antisymmetric for ortho-hydrogen (I ϭ 1) and symmetric for para-hydrogen (I ϭ 0). For an isolated hydrogen molecule rot is given by spherical harmonics, Y J mj , with the symmetry restrictions that J is odd for ortho-hydrogen and even for parahydrogen. These species are very stable and do not intermix for isolated molecules. For solid hydrogen the rotational states are only slightly perturbed from the gaseous state, and rot is still accurately described by spherical harmonics.The equilibrium ortho-hydrogen concentration is easily calculated by using the rotational energy of a diatomic simple rotator E rot ϭ BJ(J ϩ 1), where B ϭ 59.3 cm Ϫ1 is the rotational constant for hydrogen (7), and assuming a Boltzmann distribution. The equilibrium concentration of ortho-hydrogen drops from 75% at room temperature, to 61% at 100 K, to 0.1% at 20 K (7). While ortho-para conversion is strictly forbidden for isolated molecules, conversion does occur in the solid. At ambient pressure ortho-para conversion in the solid is very slow, taking weeks for a sample to equilibrate (7,8). Although there have been numerous e...

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“…The frequency range of this Raman mode is extremely large, from 36 cm −1 at zero pressure [19][20][21][22][23][24][25][26][27] to 1100 cm −1 at 250 GPa. The Raman spectrum of solid molecular deuterium has been measured up to ∼200 GPa [19][20][21][22][23]28,29 . These measurements show that hcp-based structures are stable in this pressure range.…”

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Equation of state and Raman-activeE2glattice phonon in phases I, II, and III of solid hydrogen and deuterium

et al. 2012

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We present results of lattice dynamics calculations of the P − V equation of state and the pressure dependence of the Raman-active E2g lattice phonon for p−H2 and o−D2 in a wide pressure range up to ∼2 Mbar using our recently developed semi-empirical many-body potential, and densityfunctional theory. Comparison with existing body of experimental and theoretical results showed that the employed many-body potential is a reliable basis for high-precision calculations for phases I, II, and III of solid hydrogens.PACS numbers: 64.30. Jk, 78.30.Am An accurate determination of the equation of state (EOS) of solid hydrogens has been an important research objective for decades. Systematic high-pressure studies were started in the seventies of the last century 1-3 (see reviews 4-6 and references therein). At present these x-ray and neutron studies span the pressure range up to ∼2 Mbar 7-15 and temperature range up to 1000 K. The highest compression reached in the EOS experiments is 10.4 for solid H 2 15 (7.6 for solid D 2 14 ), essentially higher than that for solid helium (8. 4) 16 . The EOS data provide a fundamental basis for examining intermolecular interactions, and for testing ab initio theories. A number of model intermolecular potentials 17,18 have been proposed based on the experimental EOS data. Another experimental technique which complements x-ray and neutron diffraction by providing direct information on intermolecular interactions and vibrational dynamics is Raman scattering. The hcp structure has a Raman-active optical mode (E 2g symmetry) in the phonon spectrum which corresponds to the out-of-phase shear motions in the two orthogonal directions in the ab plane. The frequency range of this Raman mode is extremely large, from 36 cm −1 at zero pressure 19-27 to 1100 cm −1 at 250 GPa. The Raman spectrum of solid molecular deuterium has been measured up to ∼200 GPa [19][20][21][22][23]28,29 . These measurements show that hcp-based structures are stable in this pressure range. The calculations of the E 2g Raman frequency ν(P ) using various empirical potentials 5,22,23 show that the result is highly sensitive to details of the potential used. Therefore, comparing the calculated and experimental ν(P ) is a hard test for any empirical potential (or for any other theoretical method, e.g. ab initio calculations). It is essential that these properties are sensitive to different characteristics of the intermolecular potential: while EOS is sensitive to the potential well depth, the Raman scattering experiment probes the second derivative of the potential at the minimum. In our recent paper 30 we have proposed new semi-empirical isotropic potentials for H 2 and D 2 . Unlike the previous potentials 12,17,18,31 they include not only pair forces, but triple forces as well. The goal of the present paper is to perform detailed calculations of the EOS and pressure dependence of Raman frequencies for H 2 and D 2 using our new potentials and to compare the results to available experimental data and theoretical results for...

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Raman Spectrum of Solid Orthodeuterium to 150 kbar at 5 K

Cited by 23 publications

References 13 publications

New Low-Temperature Phase of Molecular Deuterium at Ultrahigh Pressure

New Low-Temperature Phase of Molecular Deuterium at Ultrahigh Pressure

Pressure-enhanced ortho-para conversion in solid hydrogen up to 58 GPa

Equation of state and Raman-activeE2glattice phonon in phases I, II, and III of solid hydrogen and deuterium

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