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  • Articles  (259)
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  • American Institute of Physics (AIP)  (259)
  • 1985-1989  (259)
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  • 1970-1974
  • 1989  (259)
  • 1984
  • Chemistry and Pharmacology  (259)
  • 1
    Electronic Resource
    Electronic Resource
    Symmetry breaking in HCl and DCl dimers: A direct near-infrared measurement of interconversion tunneling rates (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4418-4419 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interconversion tunneling frequencies for (HCl)2 and (DCl)2 are obtained from near-infrared absorption spectra of the H(D)Cl stretching transitions, to spectroscopic precision for the mixed 35Cl–37Cl dimers. A phenomenological model of the interconversion process explains several experimental observations, and provides good estimates of the splittings expected for the 35Cl–35Cl and 37Cl–37Cl species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456774
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  • 2
    Electronic Resource
    Electronic Resource
    Dimensional scaling as a symmetry operation (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7791-7796 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The scaling of the Schrödinger equation with spatial dimension D is studied by an algebraic approach. For any spherically symmetric potential, the Hamiltonian is invariant under such scaling to order 1/D2. For the special family of potentials that are homogeneous functions of the radial coordinate, the scaling invariance is exact to all orders in 1/D. Explicit algebraic expressions are derived for the operators which shift D up or down. These ladder operators form an SU(1,1) algebra. The spectrum generating algebra to order 1/D2 corresponds to harmonic motion. In the D→∞ limit the ladder operators commute and yield a classical-like continuous energy spectrum. The relation of supersymmetry and D scaling is also illustrated by deriving an analytic solution for the Hooke's law model of a two-electron atom, subject to a constraint linking the harmonic frequency to the nuclear charge and the dimension.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457247
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio determination of mode coupling in HSSH: The torsional splitting in the first excited S–S stretching state (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5905-5909 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A mechanism for the enhanced splitting detected in the millimeter-wave rotational spectra of the first excited S–S stretching state of HSSH (disulfane) has been studied. The mechanism, which involves a potential coupling between the first excited S–S stretching state and excited torsional states, has been investigated in part by the use of ab initio theory. Based on an ab initio potential surface, coupling matrix elements have been calculated, and the amount of splitting has then been estimated by second-order perturbation theory. The result, while not in quantitative agreement with the measured splitting, lends plausibility to the assumed mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457459
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  • 4
    Electronic Resource
    Electronic Resource
    Nature of the transformations of ice I and low-density amorphous ice to high-density amorphous ice (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 7187-7192 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The changes of enthalpy at the irreversible transformation of high-density amorphous ice to low-density amorphous ice and of low-density amorphous ice to ice Ih have been measured in a Tian–Calvet heat-flow calorimeter. The equilibrium pressures of the two transformations have been estimated from the measured enthalpy and volume changes, neglecting the unknown, but small, entropy changes, as about 5 and 2 kbar, respectively. The course of the transformations has been followed in a piston-cylinder apparatus having an internal diameter of either 50 or 12 mm. The transformations are extraordinarily sharp when they are done slowly, the transformation pressure being constant to ±50 bar in 5 or 10 kbar in several transformations, although sometimes a sample transformed in two steps that were a few hundred bars apart. It seems that the activation volumes of the transformations are large and negative, and so the mechanism of the transformations is highly cooperative.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457285
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  • 5
    Electronic Resource
    Electronic Resource
    Site selective spectroscopy and crystal field analysis of Eu3+ doped lanthanum–calcium–zirconium–silicon borate (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2856-2864 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The fluorescence of Eu3+ doped lanthanum–calcium–zirconium–silicon borate ceramic was studied at 77 and 300 K using laser excited site selective spectroscopy. The fluorescence spectrum excited at 514.532 nm reveals the presence of three distinct sites for Eu3+. The sites were assigned to Eu3+ substituting for lanthanum in a ninefold coordination site in LaBO3 and Eu3+ substituting for Ca2+ in six- and sevenfold coordination sites in Ca2B2O5. To assign the spectra to the definite sites a phenomenological crystal field analysis was conducted, using C2v symmetry. The crystal field for Eu3+ in Ca2B2O5 was found to be dominated by electrostatic effects. The large 7F1 level splitting and the value of the B20 parameter support the concept of strong ionic bonding between europium and oxygen in Ca2B2O5.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455938
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  • 6
    Electronic Resource
    Electronic Resource
    Evidence for valence hole localization in the Auger decay and fragmentation of carbon and silicon tetrafluorides (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2162-2166 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Monochromatic synchrotron radiation was used to excite selectively core electrons of the carbon and fluorine atoms in carbon tetrafluoride and silicon and fluorine in silicon tetrafluoride. The fragmentation processes were examined using time-of-flight mass spectroscopy. The mass spectra show the distribution of ions collected in coincidence with low and high energy electrons. Distinct changes in the mass spectra with atomic site of excitation and photon energy are observed. The observation of F2+ ions following fluorine 1s excitation in SiF4 provides significant evidence for a "valence bond depopulation'' mechanism involving the formation of a localized, two-hole final state that persists on the time scale of fragmentation. In contrast, no F2+ was observed for CF4, which indicates that fragmentation for this molecule is more characteristic of a delocalized two-hole state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456011
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  • 7
    Electronic Resource
    Electronic Resource
    Transformation of ice VIII to amorphous ice by "melting'' at low temperature (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2390-2392 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The melting curve of ice VIII near 25 kbar, which has a positive slope, has been estimated from various thermodynamic data and extrapolated approximately to 60 K at zero pressure. When ice VIII is heated from 77 K and ambient pressure it should, therefore, "melt,'' presumably below the glass transition. It has been shown to do so, and transforms to low-density amorphous ice when heated to about 125 K at ambient pressure. Ice I, whose melting curve has a negative slope, is already known to transform to a high-density amorphous ice at 77 K and 10 kbar, and so this and the present transformation are symmetrical equivalents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455981
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  • 8
    Electronic Resource
    Electronic Resource
    Methyl torsional barriers in different electronic states. Simultaneous determination from the rotationally resolved fluorescence excitation spectrum of a large molecule (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2521-2522 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two types of splittings have been observed in the rotationally resolved fluorescence excitation spectrum of the 000 band in the S1 ←S0 electronic transition of 1-methylnaphthalene at ∼315 nm. One type is independent of J and K−1 and is produced by small differences in the A/E methyl torsional level spacings in the two electronic states. The second type is independent of J but dependent on K−1. It has its origin in a coupling of the methyl torsion with overall molecular rotation, which produces even smaller differences in the spacings of the S0 and S1 E levels. A simultaneous fit of both types of splittings yields the threefold barrier heights in the zero-point vibrational levels of both states, V3 (S0 )=295.2 and V3 (S1 )=292.6 cm−1. The ground state value of V3 is very different from that which has been reported earlier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455944
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  • 9
    Electronic Resource
    Electronic Resource
    Coherent anti-Stokes Raman spectroscopy of shock-compressed liquid nitrogen (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1368-1376 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational spectra of liquid nitrogen shock compressed to several high pressure/high temperature states were recorded using single-pulse multiplex coherent anti-Stokes Raman scattering. Vibrational frequencies, third-order susceptibility ratios, and linewidths are presented for the fundamental and several excited-state transitions. Vibrational frequencies were found to increase monotonically up to (approximate)17.5 GPa single shock and (approximate)30 GPa double shock. Above these pressures, the vibrational frequencies were observed to decrease with further increases in pressure. The decrease in vibrational frequency occurs in a pressure regime where the shocked nitrogen is becoming optically opaque. The consequence of the decrease in vibrational frequency on the Grüneisen mode gamma and its effect on the N2 equation of state is discussed. The transition intensity and linewidth data suggest that thermal equilibrium of the vibrational levels is attained in less than 10 ns at these high pressures and temperatures. Finally, the measured linewidths exhibit an almost linear dependence on shock temperature, and also suggest that the vibrational dephasing time has decreased to less than 1 ps at the highest pressures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456079
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  • 10
    Electronic Resource
    Electronic Resource
    Microwave spectrum and molecular structure of the N2–H2O complex (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 700-712 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The a-type, K=0 microwave spectrum of the N2–H2O complex has been observed using a pulsed molecular beam Fabry–Perot cavity microwave spectrometer. Seven isotopic species have been studied in the range of 5–23 GHz.The N2–H2O complex exhibits tunneling motions similar to the 1→2 tunneling motion of the H2O–DOD complex which gives rise to four components for each rotational transition. The molecular constants obtained for the ground tunneling (A1) state of 14N2–HOH are: B¯=2906.9252(2) MHz, DJ =0.043 486(15) MHz, and eQq(14N)=−4.253(2) MHz. The structure has a nearly linear N–N–HO geometry with a N–H distance of 2.42(4) A(ring) and an OHN angle of 169° [RO–N=3.37(4) A(ring)]. The electric dipole moment along the a principal axis of inertia was determined for the 15N2–HOH species with μa =0.833(3) D.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456149
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