Molecular hydrogen internuclear distance in high-pressure fluid and solid phases at room temperature

Ulivi, Lorenzo; Zoppi, M.; Gioè, Luciano; Pratesi, G.

doi:10.1103/physrevb.58.2383

Cited by 20 publications

(10 citation statements)

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“…3 we report the effective internuclear distance r m = r −2 −1/2 = (4πµcB 0 /h) −1/2 . In the same figure, we show data referring to the gas at room temperature [21][22][23], to the isolated molecule [33] and to the low pressure solid [10]. The marked decrease of the internuclear distance, already seen in ref.…”

mentioning

confidence: 67%

The S ₀ (0) structure in highly compressed hydrogen and the orientational transition

Grazzi¹,

Moraldi

Ulivi

2004

Europhys. Lett.

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High-pressure and shock wave effects in solids. PACS. 78.30.-j -Infrared and Raman spectra and scattering. PACS. 34.20.-Gj -Atomic and molecular collision processes and interaction: Intermolecular and atom-molecule potentials and forces.Abstract. -A calculation of the rotational S0(0) frequencies in high pressure solid parahydrogen is performed. Convergence of the perturbative series at high density is demonstrated by the calculation of second and third order terms. The results of the theory are compared with the available experimental data to derive the density behaviour of structural parameters. In particular, a strong increase of the value of the lattice constant ratio c/a and of the internuclear distance is determined. Also a decrease of the anisotropic intermolecular potential is observed which is attributed to charge transfer effects. The structural parameters determined at the phase transition may be used to calculate quantum properties of the rotationally ordered phase.The phase diagrams of hydrogen and deuterium demonstrate amazing phenomena caused by the quantum nature of both translations and rotations of the molecules in these solids [1,2]. At low pressure, both systems have an hexagonal close packed (hcp) structure, with almost freely rotating molecules [3]. A transition to a broken symmetry phase where the molecules are oriented, and the equivalence of the sites is lost (BSP or phase II) occurs for low temperature at 28 GPa for D 2 and 110 GPa for H 2 . [4-6] An appropriate description of the BSP is still lacking. The correct quantum treatment of nuclei is indeed crucial for the description of the BSP transition, given the extremely large isotopic effect on the transition pressure. For this reason a description on the basis of a molecular interaction potential offers numerous advantages with respect to, for example, ab initio molecular dynamics [7] (which generally treats the nuclear motion as classical), quantum Monte Carlo techniques (limited to zero temperature), [8] or other more sophisticated computation techniques, still prohibitive for heavy computer time needed [9]. An effective potential model for the anisotropic molecular interaction in the solid has never been derived, especially because a reliable theory to derive solid spectroscopic data was lacking.

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mentioning

confidence: 67%

The S ₀ (0) structure in highly compressed hydrogen and the orientational transition

Grazzi¹,

Moraldi

Ulivi

2004

Europhys. Lett.

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“…The 3 low-frequency bands (358, 589, and 815 cm Ϫ1 ) are easily identified as the S 0 (0), S 0 (1), and S 0 (2) rotational bands of H 2 (30). The comparison with a compressed H 2 /Ar mixture (top spectrum of After the last irradiation, the sample is monitored for several hours by measuring the Raman spectrum of different regions without observing any change in the reaction products composition.…”

Section: Resultsmentioning

confidence: 99%

High-pressure photodissociation of water as a tool for hydrogen synthesis and fundamental chemistry

Ceppatelli¹,

Bini²,

Schettino³

2009

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

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High-pressure methods have been demonstrated to be efficient in providing new routes for the synthesis of materials of technological interest. In several molecular compounds, the drastic pressure conditions required for spontaneous transformations have been lowered to the kilobar range by photoactivation of the reactions. At these pressures, the syntheses are accessible to large-volume applications and are of interest to bioscience, space, and environmental chemistry. Here, we show that the short-lived hydroxyl radicals, produced in the photodissociation of water molecules by near-UV radiation at room temperature and pressures of a few tenths of a gigapascal (GPa), can be successfully used to trigger chemical reactions in mixtures of water with carbon monoxide or nitrogen. The detection of molecular hydrogen among the reaction products is of particular relevance. Besides the implications in fundamental chemistry, the mild pressure and irradiation conditions, the efficiency of the process, and the nature of the reactant and product molecules suggest applications in synthesis.high-pressure chemistry ͉ photocatalysis T he application to molecular systems of suitable external pressures causes a density increase that determines a strengthening of the intermolecular interactions leading first to changes in the aggregation state of the material, and then to crystalline phase transitions (1). Upon further compression, the possible overlap of the electronic density of nearest-neighbor molecules can also trigger a complete reconstruction of the chemical bonds, giving rise to new materials in some cases recoverable at ambient conditions (2). After the pioneering work on the pressure-induced polymerization of cyanogen (3) and acetylene (4) crystals, several simple molecular crystals have been reported to react upon application of suitable external pressure, giving rise to high-quality polymeric (5-7) and amorphous (8-10) materials of potential technological interest. These transformations require pressures from several to 100 GPa, as in the nitrogen case (7), but the reaction threshold pressure has been successfully lowered in almost all of the unsaturated hydrocarbons studied so far by a photoactivation of the high-pressure reactions (11). In some cases, an increasing selectivity (5) or the opening of new reaction paths (12) is also observed. These syntheses are appealing because only physical methods are used, thus representing an interesting perspective for a green chemistry (13).The mechanisms governing the photoinduced reactivity of molecular systems derive from the structural and charge density distribution changes after an electronic transition. In general, the excited molecule is characterized by a reduced binding order that determines molecular bonds stretching, a lowering of rotational and torsional barriers, an increase in the polarity, and even dissociation and ionization. These species can be particularly aggressive from a chemical point of view and, depending on their lifetime and free mean path, can trigger a...

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“…The Raman spectra of the bubbles in the 200-1200 cm À1 frequency region (Figure 2 A) are dominated by four sharp bands, identified as the S 0 (0) (355 cm À1 ), S 0 (1) (589 cm À1 ), S 0 (2) (816 cm À1 ), and S 0 (3) (1033.5 cm À1 ) rotational bands of H 2 . [23] Other product bands, broader and weaker, which are the only signals observed in the transparent areas, also appears in some bubbles (traces e, h, and l). The Raman spectra of the transparent areas in the 200-1200 cm À1 frequency region show product bands with peak frequencies measured at 428, 526, 805, 898, 941, 1005 (shoulder), 1022, and 1135 cm À1 (Figure 2 B, traces d, x, y, and z).…”

Section: Matteo Ceppatelli* Roberto Bini Maria Caporali and Maurizmentioning

confidence: 92%

High‐Pressure Chemistry of Red Phosphorus and Water under Near‐UV Irradiation

et al. 2013

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Molecular hydrogen internuclear distance in high-pressure fluid and solid phases at room temperature

Cited by 20 publications

References 14 publications

The S ₀ (0) structure in highly compressed hydrogen and the orientational transition

The S ₀ (0) structure in highly compressed hydrogen and the orientational transition

High-pressure photodissociation of water as a tool for hydrogen synthesis and fundamental chemistry

High‐Pressure Chemistry of Red Phosphorus and Water under Near‐UV Irradiation

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Molecular hydrogen internuclear distance in high-pressure fluid and solid phases at room temperature

Cited by 20 publications

References 14 publications

The S 0 (0) structure in highly compressed hydrogen and the orientational transition

The S 0 (0) structure in highly compressed hydrogen and the orientational transition

High-pressure photodissociation of water as a tool for hydrogen synthesis and fundamental chemistry

High‐Pressure Chemistry of Red Phosphorus and Water under Near‐UV Irradiation

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The S ₀ (0) structure in highly compressed hydrogen and the orientational transition

The S ₀ (0) structure in highly compressed hydrogen and the orientational transition