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  • 1
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 140, No. 22 ( 2014-06-14)
    Abstract: Low-energy excitations of a single water molecule are studied when confined within a nano-size cavity formed by the ionic crystal lattice. Optical spectra are measured of manganese doped beryl single crystal Mn:Be3Al2Si6O18, that contains water molecules individually isolated in 0.51 nm diameter voids within the crystal lattice. Two types of orientation are distinguished: water-I molecules have their dipole moments aligned perpendicular to the c axis and dipole moments of water-II molecules are parallel to the c-axis. The optical conductivity σ(ν) and permittivity ɛ′(ν) spectra are recorded in terahertz and infrared ranges, at frequencies from several wavenumbers up to ν = 7000 cm−1, at temperatures 5–300 K and for two polarizations, when the electric vector E of the radiation is parallel and perpendicular to the c-axis. Comparative experiments on as-grown and on dehydrated samples allow to identify the spectra of σ(ν) and ɛ′(ν) caused exclusively by water molecules. In the infrared range, well-known internal modes ν1, ν2, and ν3 of the H2O molecule are observed for both polarizations, indicating the presence of water-I and water-II molecules in the crystal. Spectra recorded below 1000 cm−1 reveal a rich set of highly anisotropic features in the low-energy response of H2O molecule in a crystalline nano-cavity. While for E∥c only two absorption peaks are detected, at ∼90 cm−1 and ∼160 cm−1, several absorption bands are discovered for E⊥c, each consisting of narrower resonances. The bands are assigned to librational (400–500 cm−1) and translational (150–200 cm−1) vibrations of water-I molecule that is weakly coupled to the nano-cavity “walls.” A model is presented that explains the “fine structure” of the bands by a splitting of the energy levels due to quantum tunneling between the minima in a six-well potential relief felt by a molecule within the cavity.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2014
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 2
    In: Journal of Applied Physics, AIP Publishing, Vol. 114, No. 2 ( 2013-07-14)
    Abstract: Terahertz and infrared spectra of the optical response of DyScO3 single crystal are measured at temperatures from 5 K to 300 K for two different polarizations E‖[1¯01] and E‖[010] , i.e., along the two crystallographic directions of the DyScO3 substrates used for growing of thin films and heterostructures. Detailed reference data on the terahertz dielectric characteristics of the DyScO3 substrate are presented. We discuss the mechanisms responsible for electromagnetic absorption. Phonon spectra are analyzed along with the results of group-theoretical analysis of the crystal structure. Besides phonon modes, additional resonance absorptions are found and assigned to the electronic transitions between Kramers doublets in the three lowest-energy terms of the Dy3+ ion.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2013
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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