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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5313-5315 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ν3 (O–Si stretch) fundamental bands of the HOSi+ and DOSi+ molecular ions in the 9 μm region have been detected for the first time, using a tunable infrared diode laser spectrometer and a hollow cathode discharge cell. Analysis of the results yielded accurate values for the molecular rotational and centrifugal distortion parameters, as well as for the band origins, which are 1127.009 cm−1 for HOSi+ and 1103.112 cm−1 for DOSi+ . The ground vibrational state parameters are in excellent agreement with those determined from the ν1 bands of the two isotopes.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 7273-7286 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Precise measurements of the frequencies of a number of new rotational transitions of a 3Π CO (v=0–4) in the range 250–500 GHz are reported. In addition earlier measurements of the J=0–1 frequencies near 90 GHz have been repeated at higher precision and extended to include the v=6 lines. The nonlinear least-squares analysis of this microwave data combined with the lambda doublet transition frequencies of Klemperer and co-workers was carried out for v=0–4 by direct diagonalization of a Hamiltonian matrix that included the relevant v subblock of the a 3Π state along with the subblocks for v'=0–10 of the a' 3Σ+ state. The new frequencies make possible the determination from the rf-microwave data set of several parameters that previously had to be assumed, and the method of treating most of the a–a' perturbations directly in the large matrix yields parameters, especially lambda doubling constants, which vary less, but more smoothly, with J than before. The later smoothness is found to be enhanced by inclusion of an off-diagonal, spin–spin interaction in the a–a' perturbation Hamiltonian, as was done in published fits of FTIR spectra of the a' 3Σ+–a 3Π system. We also discuss the theory of the perturbed Zeeman effect of a 3Π CO, along with some preliminary measurements, and report a value of the pressure broadening parameter for a typical rotational transition in this state.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5310-5312 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ν1 (H–O) stretches of HOSi+ and DOSi+ have been observed with the difference frequency laser system in the hollow cathode discharge. The ions were observed either by discharge of (CH3)3SiOH or (CH3)3SiOD in a buffer containing H2 (or D2) and He, or by discharging SiH4 and N2O in a buffer of H2 or H2 and He. Discharging SiH4 and H2O in buffers of H2 and H2 and He was not successful in producing HOSi+. The constants obtained were: ν0=3662.364 67(15) cm−1, B000=18 260.75(22) MHz, D000=20.44(31) kHz, B100=18 195.05(23) MHz, and D100=19.91(34) kHz for HOSi+. For DOSi+ we obtained: ν0=2716.558 13 (12) cm−1, B000=16 231.05(24) MHz, D000=15.69(38) kHz, B100=16 154.41(22) MHz, and D100=15.60(33) kHz. These values agree well with the theory. The combination of the two B0 values results in r0(H–O)=0.940 A(ring) and r0(O–Si) =1.537 A(ring). The differences between these values and the calculated equilibrium values are similar to the corresponding results for HOC+.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1712-1716 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The gas phase C2D absorption spectrum has been studied in the 2800 cm−1 region using a high resolution difference-frequency laser spectrometer. The C2D molecules were produced in a hollow cathode discharge in a mixture of C2H2 or C2D2 (∼20 mTorr) and D2 (∼400 mTorr). Two bands were identified and rotationally analyzed. One band at 2796 cm−1 was found to be a 2Π–2Σ+ transition with the lower state being the ground state. The upper level of this band is assigned to the (110) state in the ground electronic state, X˜ 2Σ+. The other band at 2851 cm−1 is a 2Σ+–2Σ+ transition from the (001) state in X˜ 2Σ+ to a vibronic 2Σ+ state which was found to be perturbed. Accurate molecular constants for the upper levels involved were determined from least-squares fit. These constants as well as the observed transition frequencies are reported.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4008-4013 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using classical elasticity theory, the rise in free energy upon crosslinking nematogenic polymers into a network is calculated for the isotropic and nematic phases. Spontaneous strains are allowed for in the network. The consequence of network formation upon nematic–isotropic equilibria is calculated by adding these elastic contributions to a conventional Landau theory. Memory of the crosslinking conditions yields quartic and quadratic additions to the standard Landau theory. We find that crosslinking in the isotropic state lowers the nematic–isotropic phase transition temperature compared with the unlinked case and the application of suitable stress raises it again. Crosslinking in the nematic state raises the transition temperature. We recover the mechanical critical point proposed long ago by de Gennes. Our Gaussian theory encompasses both main- and side-chain polymers. The hairpin limit for main chain networks yields a modulus varying exponentially with temperature. The Landau–de Gennes free energy for comb polymers is presented for the first time.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1308-1313 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new microprocessor-controlled multichannel spectrometer for the measurement of fluorescence detected circular dichroism (FDCD) is presented. Spectra of model steroid compounds are provided to demonstrate the analytical utility of multichannel FDCD over the classical circular dichroism measurement. A detection limit of 3.05×10−8 M was determined for a solution of estrone based on a signal/noise ratio of 2 as a lower limit. The optics and electronics for the rapid acquisition of multichannel FDCD data are described in detail.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 32 (1991), S. 3168-3175 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The boundary of a boundary principle has been suggested by J. A. Wheeler as a realization of the austerity idea in field theories. This principle is described in three basic field theories—electrodynamics, Yang–Mills theory, and general relativity. It is demonstrated that it supplies a unified geometric interpretation of the source current in each of the three theories in terms of a generalized E. Cartan moment of rotation. The extent to which the boundary of a boundary principle represents the austerity principle is discussed. It is concluded that it works in a way analogous to thermodynamic relations and it is argued that deeper principles might be needed to comprehend the nature of austerity.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 34 (1993), S. 4050-4063 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The N=2 super W4 algebra is constructed as a certain reduction of the second Gel'fand–Dikii bracket on the dual of the Lie superalgebra of N=1 super pseudodifferential operators. The algebra is put in manifestly N=2 supersymmetric form in terms of three N=2 superfields Φi(X), with Φ1 being the N=2 energy momentum tensor and Φ2 and Φ3 being conformal spin 2 and 3 superfields, respectively. A search for integrable hierarchies of the generalized Korteweg-de Vries (KdV) variety with this algebra as Hamiltonian structure gives three solutions, exactly the same number as for the W2 (super KdV) and W3 (super Boussinesq) cases.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 33 (1992), S. 2242-2248 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The geometric construction of the E. Cartan moment of rotation associated to the spacetime curvature provides a geometric interpretation of the gravitational field sources and describes geometrically how the sources are "wired'' to the field in standard geometrodynamics. The E. Cartan moment of rotation yields an alternate way (as opposed to using variational principles) to obtain Einstein equations. The E. Cartan construction uses, in an essential way, the soldering structure of the frame bundle underlying the geometry of the gravitational field of general relativity. The geometry of Ashtekar's connection formulation of gravitation is based on a complex-valued self-dual connection that is not defined on the frame bundle of spacetime. It is shown how to transfer the construction of the E. Cartan moment of rotation of Ashtekar's formulation of the theory of gravity and demonstrate that no spurious equations are produced via this procedure.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 33 (1992), S. 758-770 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: Results are presented concerning the structure on the real line of the "universal function'' which is the fixed point solution of the Feigenbaum–Cvitanovic renormalization group equation associated with period-doubling chaos in quadratic maps. It is shown that the values which the function takes at its turning points can be algebraically characterized by relation to the infinite cycle associated with the original turning point of the map on the interval. These extrema become increasingly numerous as the argument increases, and their locations can be found progressively using knowledge of the previously determined extrema. As well as providing a simple understanding of the structure of the universal function these simple observations may be of assistance in investigating the convergence or asymptotic behavior of approximations to the universal function, and perhaps in providing a "corrector'' step to some of these schemes.
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