Equilibrium orientations of diatomic-molecular impurities in cubic crystals determined by a polarized Raman study of the stretching mode

Fleurent, Hilde; Joosen, W.; Schoemaker, D.

doi:10.1103/physrevb.38.6257

Cited by 13 publications

(5 citation statements)

References 42 publications

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“…A later analysis of the polarized Raman spectra with the behavior type method 19 confirmed that the molecular orientation is close to ͗100͘, although allowing for the possibility that it slightly deviates from this. 12 Suto and Ikezawa 20 determined ⌬ 1 ϭ1.85 cm Ϫ1 and ⌬ 2 ϭ3.41 cm Ϫ1 with millimeter wave absorption spectroscopy. To explain the energy-level structure, they made a linear combination of atomic orbitals-molecular-orbital ͑LCAO-MO͒ calculation in which the center of mass of the OH Ϫ moves between six off-center positions with potential wells of elliptic shape.…”

Section: A Review Of Previous Workmentioning

confidence: 99%

Infrared and Raman studies of hydroxide ions in NaCl extended toH→Dand16<

et al. 2001

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Substitutional OH Ϫ and OD Ϫ defects in NaCl have been studied with Fourier-transform infrared ͑FTIR͒ and polarized Raman-scattering ͑RS͒ spectroscopy. For the first time, the motional levels of the OH Ϫ were clearly resolved in their stretch-mode ͑SM͒ absorption spectra, showing no change in splitting under 16 OH Ϫ → 18 OH Ϫ isotope exchange. Due to extremely small oscillator strengths, the first harmonic SM absorptions of 16 OD Ϫ and 18 OD Ϫ defects were not detectable. In contrast to this, the almost equal RS strengths of OH Ϫ and OD Ϫ defects permitted their detailed comparative investigation with polarized Raman scattering. The resulting low-frequency motional levels of OD Ϫ in both ground and excited SM states are found to be quite different from those of OH Ϫ and are hard to reconcile with some of the existing models. A reasonably good fit of the OH Ϫ and OD Ϫ data can be achieved with a simple V 4 Devonshire model; this suggests hindered rotation of a strongly off-center shifted center of mass in a potential with smaller energy barriers for OD Ϫ compared to OH Ϫ . Despite the unexplained weakness of the first harmonic SM absorption of OD Ϫ , phonon and librational sidebands are observed with almost similar strength as those of OH Ϫ . Their symmetry was determined by polarized RS and/or FTIR absorption measurements under uniaxial stress alignment. The ''normal'' OH Ϫ /OD Ϫ isotope shift of the librational sideband and the observation of its second harmonic show that this angular motion occurs around the center of mass in a strong and nearly harmonic potential.

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Section: A Review Of Previous Workmentioning

confidence: 99%

Infrared and Raman studies of hydroxide ions in NaCl extended toH→Dand16<

et al. 2001

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“…It is often complicated to extract symmetry information from a set of Raman spectra. A quantitative approach called the behavior type method 10 has been applied to diatomic molecules by Fleurent et al 8 The three symmetry components of the Raman spectra at 6.2 K for OH Ϫ in three hosts are displayed in Fig. 1.…”

Section: A Polarized Raman Scattering: Defect Symmetrymentioning

confidence: 99%

“…The absence of an E g spectrum and the presence of a sizable T 2g spectrum are compatible with an ͗111͘ orientation of the defects, but not with a ͗100͘ or ͗110͘ orientation. 8 In case the thermal reorientation becomes sufficiently rapid at high temperatures, the system may approach the free rotor behavior, resulting in a reduction of the T 2g intensity and the appearance of an E g spectrum. For the case of NaCl:OH Ϫ this has indeed been observed.…”

Section: A Polarized Raman Scattering: Defect Symmetrymentioning

confidence: 99%

“…Polarized Raman scattering of properly chosen symmetries of the incident and scat-tered light, can for a totally unaligned molecular defect system determine the orientation (͗100͘, ͗111͘, or ͗110͘) of the molecules. We use this ''behavior type ͑BT͒ method'' for our studied crystal-defect system 8 ͑see Sec. III A͒ and compare the results to the ones obtained by the infrared ͑IR͒ absorption dichroism for uniaxial stress-aligned molecular defects ͑see Sec.…”

Section: Introductionmentioning

confidence: 99%

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Infrared absorption and Raman scattering ofOH−andOD−stretching-

et al. 2000

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The stretching-mode ͑SM͒ of OH Ϫ and OD Ϫ defects in LiF, NaF, and KF hosts has been studied with Raman scattering and Fourier transform infrared ͑FTIR͒ absorption spectroscopy, at temperatures from 4 K to 500 K. In all three hosts the ͗111͘ orientation of the OH Ϫ molecular axis is confirmed both by polarized Raman spectra and by stress-induced FTIR dichroism. The latter technique also yields the values of the disc-shaped elastic dipole tensor, aligning the OH Ϫ parallel to an applied ͗111͘ uniaxial stress with a Curie law. Accurate band-shape analysis of low-temperature FTIR absorption and T 2g Raman spectra yields for low concentrations of OH Ϫ in LiF and KF consistent values of their nearest-neighbor reorientational tunneling parameters (⌬ϭ1.2 and 0.6 cm Ϫ1 , respectively͒. For OH Ϫ in NaF and for OD Ϫ in all three hosts spectral substructure from tunneling is undetectable in the narrow Lorentzian-shaped SM lines. The strong temperature broadening that occurs for the SM absorption and T 2g Raman bands and the smaller broadening of the A 1g line can be fitted with models for the dephasing of the transition by phonons, considering the presence of isotropic and anisotropic dephasing components. In spite of the very different amplitudes of the OH Ϫ and OD Ϫ SM vibrations, their relative infrared absorption and Raman intensities are found to be very similar; the only exception is an extremely weak oscillator strength of the OD Ϫ absorption in KF.

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“…Nevertheless, experimental reports on the optical properties of these dimer centres in different alkali halide host lattices have been published throughout the years [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. More complicated aggregate centres involving ns 2 substitutional ions have also been observed [27][28][29][30]. Knowledge of just the absorption/emission properties does not permit one to make definite statements about the geometric structure of the defect complex, however.…”

Section: Introductionmentioning

confidence: 99%

Local structures and relative stabilities of Tl⁺-dimer substitutional impurity centres in NaI and KI

Aguado¹

2001

J. Phys.: Condens. Matter

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The local lattice distortions around a Tl+-dimer substitutional impurity in NaI and KI have been investigated by using a mixed ab initio/parametrized methodology. One important conclusion of the work is that an explicit consideration of these distortions up to at least the first four coordination shells of ions around the impurity is needed in order to achieve a converged result for the first- and second-shell distortions. After describing the lattice distortions induced by both D4h and D2h configurations, we analyse their relative stability by calculating the defect formation energies. It is found that the D4h configuration is lower in energy for both crystals, but the energy difference is so small in the case of the NaI host lattice that the two configurations can be considered degenerate for all practical purposes. It is also found that inclusion of polarization interactions is crucial in the stabilization of the defect in NaI.

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Equilibrium orientations of diatomic-molecular impurities in cubic crystals determined by a polarized Raman study of the stretching mode

Cited by 13 publications

References 42 publications

Infrared and Raman studies of hydroxide ions in NaCl extended toH→Dand16<

Infrared and Raman studies of hydroxide ions in NaCl extended toH→Dand16<

Infrared absorption and Raman scattering ofOH−andOD−stretching-

Local structures and relative stabilities of Tl⁺-dimer substitutional impurity centres in NaI and KI

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Equilibrium orientations of diatomic-molecular impurities in cubic crystals determined by a polarized Raman study of the stretching mode

Cited by 13 publications

References 42 publications

Infrared and Raman studies of hydroxide ions in NaCl extended toH→Dand16<

Infrared and Raman studies of hydroxide ions in NaCl extended toH→Dand16<

Infrared absorption and Raman scattering ofOH−andOD−stretching-

Local structures and relative stabilities of Tl+-dimer substitutional impurity centres in NaI and KI

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Product

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Local structures and relative stabilities of Tl⁺-dimer substitutional impurity centres in NaI and KI