Effect of density on the induced near infrared absorption spectrum of solid parahydrogen

Jean‐Louis, M.

doi:10.1016/0009-2614(77)80396-5

Cited by 6 publications

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“…Three bands are well resolved in the frequency range 4000-6500 cm" 1 . Comparisons with low-pressure measurements [14][15][16] show that the first band arises from the excitation of a Q\(\) intramolecular stretching mode (vibron). The second band [Q\(\) + S\(0)] is due to the simultaneous creation of a Q\{\) vibron and a S\(0) rotational excitation (roton), while the third band IQRU)] arises from the excitation of a vibron and a lattice mode (phonon).…”

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“…Because of the sensitivity of the spectra to the range and extent of intermolecular interactions [1], infrared measurements of hydrogen as a function of pressure assume a critical role for determining the variation in such interactions with density. Such measurements have been performed to moderate pressures [15,16], but none has yet been conducted in the megabar range ( > 100 GPa).…”

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Synchrotron infrared spectroscopy at megabar pressures: Vibrational dynamics of hydrogen to 180 GPa

et al. 1992

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We have developed new techniques for measuring infrared spectra at megabar pressures using synchrotron radiation and applied them to study the Q\(\), Q\(\)+S\(0), and QRU) vibrational transitions of solid hydrogen to 180 GPa. The frequency difference between the Q\(\) infrared and Raman vibrons increases from 3 cm" 1 (zero pressure) to 510 cm" 1 (180 GPa), indicating a dramatic increase in intermolecular coupling with pressure. A negative frequency shift is observed for the infrared vibron above 140 GPa. A significant increase in frequency and LO-TO splitting of the lattice phonon is also documented. PACS numbers: 78.30.Hv, 62.50.+p, 63.20.-eThe density dependence of intermolecular and intramolecular interactions in solid hydrogen is fundamental to understanding the range of structure, dynamics, and phase transitions in this material, from quantumsolid behavior of the low-density molecular solid to theoretically predicted monatomic phases at ultrahigh pressures [1]. One of the critical issues is the mechanism responsible for the decrease in the frequency of the Raman-active (intramolecular) vibron at 30 GPa in hydrogen and 50 GPa in deuterium [2-4]. The negative pressure shift continues to higher pressures above 100 GPa [5-7]. This result has been ascribed to the development of increasing intermolecular and decreasing intramolecular bonding with pressure, and has been regarded as a possible precursor to dissociation. In the megabar range (> 100 GPa), profound changes in interactions are expected due to the onset of band-overlap metallization and related transitions [8]. Further evidence for changes in intermolecular forces with pressure has been obtained from calculations of pressure-volume relations using gasphase (or low-density) intermolecular potentials for hydrogen [9], which show a significant departure from accurate equations of state determined by diffraction techniques [10]. Moreover, the phonon frequencies calculated from such potentials differ significantly from direct measurements by Raman spectroscopy [8,11]. These results demonstrate that although appreciable increases in intermolecular interactions occur with increasing density, the form of the potentials and a quantitative understanding of the vibrational dynamics in the high-density solid are not yet in hand.Additional types of vibrational spectroscopic measurements are required to evaluate separately the intramolecular and intermolecular interactions. Raman studies of H2 and D2 molecules isolated in rare-gas matrices and of hydrogen isotopic mixtures provide such information, but these have been limited to moderate pressures [12,13]. The infrared absorption spectrum of solid hydrogen consists of vibrational and rotational transitions induced by fluctuating dipole moments that arise from intermolecular interaction in condensed phase [1]. The infrared absorption spectrum of solid hydrogen at ambient pressure has been measured in detail by Gush et al. [14]. Because of the sensitivity of the spectra to the range and extent of intermolecular interact...

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confidence: 99%