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  • 1
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    A cryogenic rotation stage with a large clear aperture for the half-wave plates in the Spider instrument (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-01-09
    Description: We describe the cryogenic half-wave plate rotation mechanisms built for and used in Spider , a polarization-sensitive balloon-borne telescope array that observed the cosmic microwave background at 95 GHz and 150 GHz during a stratospheric balloon flight from Antarctica in January 2015. The mechanisms operate at liquid helium temperature in flight. A three-point contact design keeps the mechanical bearings relatively small but allows for a large (305 mm) diameter clear aperture. A worm gear driven by a cryogenic stepper motor allows for precise positioning and prevents undesired rotation when the motors are depowered. A custom-built optical encoder system monitors the bearing angle to an absolute accuracy of ±0.1 ∘ . The system performed well in Spider during its successful 16 day flight.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 2
    Electronic Resource
    Electronic Resource
    An ab initio semirigid bender calculation of the rotation and trans-tunneling spectra of (HF)2 and (DF)2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5154-5159 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a purely ab initio minimum energy path for the trans-tunneling motion in the HF dimer, the energy levels for the K-type rotation and trans-tunneling motion for (HF)2 and (DF)2 are calculated with a one-dimensional semirigid bender Hamiltonian and no adjustable parameters. The transition moments for rotation-tunneling transitions are calculated, using our ab initio value for the dipole moment of an isolated HF molecule, and we also calculate B¯ values. The energy levels we obtain are in close agreement with experiment; for example, the K=0 tunneling splitting in (HF)2 is calculated as 0.65 cm−1 compared to the experimental value of 0.658 69 cm−1. As well as showing that our ab initio minimum energy path is very good, the calculation demonstrates that the semirigid bender formalism is able to account quantitatively for the unusual K dependence of the rotational energies resulting from the quasilinear behavior, and that the trans-tunneling motion is separable from the other degrees of freedom. We use the results to predict the locations, and transition moments, of the ΔK=0 and ±1 subbands in the tunneling spectra of (HF)2 and (DF)2, many of which have not yet been observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457613
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Electronic transition moment variation and Einstein coefficients for the NO(B 2Π–X 2Π) system (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 7667-7676 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper details an investigation of the variation in the electronic transition moment with internuclear separation for the NO(B2Π–X2Π) transition. Measurements of the relative intensities of a number of NO B–X vibronic transitions having a common upper level were used to construct a relative transition-moment function between 1.27 and 1.60 A(ring). After normalizing this relative function by experimentally determined radiative lifetimes, the transition-moment function was extended down to 1.23 A(ring) by incorporating data from oscillator strength measurements. In contrast to empirical transition-moment functions that have been proposed previously, the function in this paper decreases with increasing internuclear separation. Unlike these other functions, however, this one is consistent with theoretical predictions, with most available oscillator strength data, and with the observed trend in B-state radiative lifetimes as a function of vibrational level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460722
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  • 4
    Electronic Resource
    Electronic Resource
    Ionization potentials and radii of atoms and ions of element 104 (unnilquadium) and of hafnium (2+) derived from multiconfiguration Dirac–Fock calculations (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8041-8050 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multiconfiguration relativistic Dirac–Fock (MCDF) values have been computed for the first four ionization potentials (IPs) of element 104 (unnilquadium) and of the other group 4 elements (Ti, Zr, and Hf). Factors were calculated that allowed correction of the systematic errors between the MCDF IPs and the experimental IPs. Single "experimental'' IPs evaluated in eV (to ±0.1 eV) for element 104 are: [104(0),6.5]; [104(1+),14.8]; [104(2+),23.8]; [104(3+),31.9]. Multiple experimental IPs evaluated in eV for element 104 are: [(0−2+),21.2±0.2]; [(0−3+),45.1±0.2]; [(0−4+),76.8±0.3]. Our MCDF results track 11 of the 12 experimental single IPs studied for group 4 atoms and ions. The exception is Hf(2+). We submit our calculated IP of 22.4±0.2 eV as much more accurate than the value of 23.3 eV derived from experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459334
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  • 5
    Electronic Resource
    Electronic Resource
    Global potential-energy surfaces for H2Cl (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3110-3120 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present two new analytic potential-energy surfaces suitable for studying the competition between the abstraction reaction H+DCl→HD+Cl and the exchange reaction H+DCl→HCl+D. In the abstraction channel the surfaces are only slightly different from the Stern–Persky–Klein GSW surface, but the exchange barrier on both surfaces is raised by inclusion of a three-center term fitted to ab initio extended-basis-set multireference configuration interaction calculations with scaled external correlation. The two surfaces differ significantly only for the steepness of H–Cl–H bend potential. The exchange and abstraction saddle points are characterized by harmonic analysis for H2Cl, HDCl, and D2Cl, and we also compute vibrationally adiabatic barrier heights including anharmonicity. We also report thermal rate constants and activation energies for both reactions mentioned above.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455914
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  • 6
    Electronic Resource
    Electronic Resource
    L2 golden rule method to calculate partial widths for the decay of resonance states (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3667-3677 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have calculated resonance energies and partial widths for two two-dimensional models of van der Waals molecule predissociation. We use a general method involving only Hamiltonian and overlap integrals in a square integrable (L 2) basis set containing a scale parameter. We use a stabilization method with a compactness criterion to find the resonance energies, and a decoupled golden rule method to find the partial widths. The results are compared to accurate energies and partial widths obtained by fitting solutions of the close-coupling equations to multichannel Breit–Wigner expressions. We studied resonances having two open channels for two sets of potential parameters, and in each case we obtained an accuracy of 16% or better for both partial widths by the L 2 method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453866
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  • 7
    Electronic Resource
    Electronic Resource
    Fermi resonances and local modes in water, hydrogen sulfide, and hydrogen selenide (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4171-4185 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A simple vibrational curvilinear internal coordinate Hamiltonian for bent H2X molecules is constracted by expanding the g matrix elements and the potential energy function in terms of the Morse variable y=1−exp(−ar) and retaining important local mode and Fermi resonance terms. The eigenvalues of this Hamiltonian are calculated variationally using Morse oscillator basis functions for the stretches and harmonic oscillator basis functions for the bend. The nonlinear least-squares method is used to optimize the potential energy parameters. The model is applied to water, hydrogen sulfide, and hydrogen selenide. Experimental vibrational levels up to 18 500 cm−1 for five symmetrical isotopic species of water are reproduced with a standard deviation of about 4 cm−1. For both hydrogen sulfide and hydrogen selenide two symmetrical isotopic species were included in the optimization procedure and standard deviations of 1.0 and 0.66 cm−1 were obtained. The potential energy parameters obtained agree well with previous anharmonic force field calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453824
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  • 8
    Electronic Resource
    Electronic Resource
    Adiabatic approach to the coupling between local- and normal-like modes (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2207-2223 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An adiabatic method of incorporating harmonic bending and stretching modes into the local mode model is developed. This is achieved by defining local normal mode coordinates which enable one to treat some of the stretches as local modes and the other vibrational degrees of freedom as normal modes in a perfectly systematic fashion. An energy level expression for a system of local modes coupled to local normal modes (harmonic oscillators) is derived. The expression has the same form as the standard normal mode formula. A simple formula for the anharmonicity constant xbs is obtained. The formulas are shown to reproduce well the experimental results for H2O, H2S, and H2Se and are tested against previous calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452119
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  • 9
    Electronic Resource
    Electronic Resource
    Quantum canonical transformation of the rotational–vibrational Hamiltonian to remove a Coriolis term (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 461-477 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A quantum mechanical rotational–vibrational Hamiltonian with one Coriolis term which couples vibration and rotation is transformed to eliminate the Coriolis term. This is achieved by employing a Bogoliubov–Tyablikov transformation. A closed-form energy level expression is obtained for the vibrational–rotational energy levels of a rigid symmetric top coupled to harmonic oscillators. For an asymmetric rotor the transformation introduces small off-diagonal matrix elements which couple vibrational states. Nearly degenerate vibrational states would be strongly coupled by the original Coriolis term, but the small off-diagonal matrix elements of the transformed Hamiltonian may be treated perturbatively to obtain an effective rotational Hamiltonian for each vibrational state. The new theoretical method is compared with variational calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460362
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  • 10
    Electronic Resource
    Electronic Resource
    Completely L2 Golden Rule method for resonance energies and widths (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 6251-6257 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have calculated the resonance energies and widths for both one-dimensional scattering resonances and a two-dimensional model of van der Waals molecule predissociation by a general method involving only Hamiltonian and overlap integrals in a single square-integrable basis set containing a scale parameter. We use a stabilization method with a compactness criterion to find the resonance energies and a generalization of the Golden Rule formalism of Macías and Riera to calculate the widths. The results are compared to accurate resonance energies and widths obtained by Breit–Wigner fits. For the final method, as applied to four cases, the errors in the resonance energies are 10−3%, 0.8%, 0.5%, and 0.03%, and the errors in the widths are 2%, 3%, 6%, and 11%, respectively. The new method has particular advantages over the analytic continuation of stabilization graphs when the density of states is high.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452462
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