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  • 1970-1974  (4)
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  • 1970-1974  (4)
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  • 1
    Online Resource
    Online Resource
    Near-Resonant Electronic Energy Transfer from Argon to Hydrogen
    AIP Publishing ; 1972
    In:  The Journal of Chemical Physics Vol. 56, No. 7 ( 1972-04-01), p. 3608-3618
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 56, No. 7 ( 1972-04-01), p. 3608-3618
    Abstract: The argon sensitized fluorescence of molecular hydrogen has been observed. Relative cross sections have been determined for transitions of the type H2(X 1Σg +,  v=0, J) + Ar* → H2(B 1Σu +,  v′, J′) + Ar + Δ E,where Ar* is either Ar 4s[112]J=1 0 or Ar 4s′[12] J=1 0 and the hydrogen molecules, H2, D2, and HD are initially thermally distributed among J states at 300 ± 30°K. Calculations indicate that the largest cross sections, on the order of gas kinetic or larger, are due primarily to long range dipole-dipole interactions. These cross sections are for transitions for which |  Δ E  |  〈 100 cm−1 when Δ J ≡ J′ − J=± 1. The long range dipolar calculations establish an absolute magnitude scale for the cross sections. A curve crossing mechanism is possible for negative ΔE and provides a plausible explanation for the remaining levels excited. Generally, only one vibrational level of the hydrogen molecule is excited by each argon state. This contrasts sharply with many previous sensitized excitation experiments in which most of the energetically accessible energy levels are excited.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1677737
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1972
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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    Online Resource
  • 2
    Online Resource
    Online Resource
    Role of Spin Symmetry Conversion in Nuclear Relaxation in Solids
    AIP Publishing ; 1971
    In:  The Journal of Chemical Physics Vol. 54, No. 9 ( 1971-05-01), p. 4044-4049
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 54, No. 9 ( 1971-05-01), p. 4044-4049
    Abstract: The rates of nuclear transitions in molecules which are able to rotate about a single axis in the solid are considered. Only the effects of intramolecular dipolar interactions are taken into account. In molecules with threefold or higher symmetry about the rotation axis, only transitions which alter the symmetry of the nuclear state can occur. In molecules with twofold symmetry, if the angle between the internuclear vector and the rotation axis is 90°, only transitions which retain the nuclear symmetry can occur. If that angle is not 90°, both nuclear transitions which alter and which conserve symmetry are allowed. The detailed mechanisms which cause these two types of nuclear transitions are similar.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1675464
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1971
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 3
    Online Resource
    Online Resource
    Nuclear Relaxation in Solids due to Molecular Rotation at Low Temperatures
    AIP Publishing ; 1970
    In:  The Journal of Chemical Physics Vol. 52, No. 5 ( 1970-03-01), p. 2534-2538
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 52, No. 5 ( 1970-03-01), p. 2534-2538
    Abstract: A quantum-mechanical treatment of nuclear spin–lattice relaxation due to molecular rotation in the solid is presented. It is shown that at low temperatures, where this treatment is valid, the rate of relaxation is directly proportional to the rates of transitions among the torsional levels and to the extent to which those transitions alter the expectation value of the diple–dipole Hamiltonian. The form of the expression for T1 is analogous to the usual form obtained by a correlation function approach, in the limit ω0τc ≫ 1, if the inverse of the correlation time is identified with an appropriate average transition rate among torsional levels. It is predicted that at very low temperatures the apparent activation energy of the correlation time should be much smaller than the height of the barrier to rotation.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1673338
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1970
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 4
    Online Resource
    Online Resource
    Interaction Potential between Ground State Helium Atom and the B  1Σ u + State of the Hydrogen Molecule
    AIP Publishing ; 1972
    In:  The Journal of Chemical Physics Vol. 56, No. 3 ( 1972-02-01), p. 1219-1223
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 56, No. 3 ( 1972-02-01), p. 1219-1223
    Abstract: In order to aid in the interpretation of the energy transfer experiments of Moore and co-workers, ab initio quantum mechanical calculations have been carried out on the four electron system 1S He+ B 1Σu+ H2. Nine C2v geometries were considered, all involving a fixed H–H separation of 2.43 bohr. A contracted Gaussian basis of three s and two p functions on each atom was used, and calculations were performed including 1, 416, and 706 configurations. The 416 configuration calculation was designed to include only the electron correlation between He and H2 and should yield the most reliable results. The 416 configuration calculation predicts a large van der Waals interaction between He and the lowest 1Σu+ state of H2. The potential curve has a well depth of 401 cm−1 (0.05 eV) and this minimum occurs for a distance 3.72 bohr (1.97 Å) between He and the H2 center of mass. SCF calculations using the same basis and geometries were done on the He+ X 1Σg+ H2 and He+b 3Σu+ systems. The potential curves for these two states lie well below that of He+B1Σu+ H2 for thermal energies and it is suggested that curve crossing with the two lower surfaces is not responsible for the observed quenching of the B1Σu+ H2 fluorescence by He.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1677348
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1972
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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