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Title: Vibrational states of a water molecule in a nano-cavity of beryl crystal lattice

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:Be{sub 3}Al{sub 2}Si{sub 6}O{sub 18}, 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 ε{sup ′}(ν) spectra are recorded in terahertz and infrared ranges, at frequencies from several wavenumbers up to ν = 7000 cm{sup −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 ε{sup ′}(ν) caused exclusively by water molecules. In the infrared range, well-known internal modes ν{sub 1}, ν{sub 2}, and ν{sub 3} of the H{sub 2}O molecule are observed for both polarizations, indicating the presence of water-I and water-II molecules in the crystal. Spectra recorded below 1000 cm{sup −1} reveal a rich set ofmore » highly anisotropic features in the low-energy response of H{sub 2}O molecule in a crystalline nano-cavity. While for E∥c only two absorption peaks are detected, at ∼90 cm{sup −1} and ∼160 cm{sup −1}, several absorption bands are discovered for E⊥c, each consisting of narrower resonances. The bands are assigned to librational (400–500 cm{sup −1}) and translational (150–200 cm{sup −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.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [3] ;  [5] ;  [6] ;  [7] ; ;  [8] ;  [1] ;  [3] ;  [9]
  1. Moscow Institute of Physics and Technology, 9 Institutskiy per., 141700 Dolgoprudny, Moscow Region (Russian Federation)
  2. (Germany)
  3. (Russian Federation)
  4. Faculty of Physics, Southern Federal University, 5 Zorge St., 344090 Rostov-on-Don (Russian Federation)
  5. Kazan Physical-Technical Institute, Russian Academy of Sciences, 10/7 Sibirsky Trakt, 420029 Kazan (Russian Federation)
  6. Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany)
  7. Institute of Laser Physics, Russian Academy of Sciences, 13/3 Ac. Lavrentyev's Prosp., 630090 Novosibirsk (Russian Federation)
  8. Institute of Geology and Mineralogy, Russian Academy of Sciences, 3 Ac. Koptyug's Prosp., 630090 Novosibirsk (Russian Federation)
  9. 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart (Germany)
Publication Date:
OSTI Identifier:
22420094
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 22; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; ANISOTROPY; BERYL; CRYSTAL LATTICES; DIPOLE MOMENTS; DOPED MATERIALS; EXCITATION; FINE STRUCTURE; MANGANESE; MOLECULES; MONOCRYSTALS; PEAKS; PERMITTIVITY; POLARIZATION; RESONANCE; SPECTRA; TUNNEL EFFECT; VIBRATIONAL STATES; WATER