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  • American Institute of Physics (AIP)  (123)
  • 1985-1989  (123)
  • 1989  (71)
  • 1985  (52)
  • 1
    Electronic Resource
    Electronic Resource
    A high-speed photomultiplier gating circuit for luminescence measurements (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 2924-2928 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high-speed, normally on, gating circuit has been developed for linear-focused photomultipliers such as the EMI 9816. The gate is capable of attenuating photomultiplier response by 〉5000:1 with a turn-off and turn-on time of 60 and 40 ns, respectively. The circuit is compact enough to fit in a standard photomultiplier housing and has low enough power consumption to run off the photomultiplier high-voltage supply. The high speed and high extinction efficiency make this gate suitable for pulse rejection in low-light level, submicrosecond, time-resolved luminescence measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140628
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  • 2
    Electronic Resource
    Electronic Resource
    A comprehensive kinetic model of the electron-beam-excited xenon chloride laser (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 5707-5725 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new kinetics model capable of simulating performance of electron-beam-pumped xenon chloride lasers over the full range of experimental evidence is presented. The model comprises 202 chemical processes employing 41 species. Its operation is described and the full set of rate equations given. Calculations of stimulated emission and absorption cross sections for XeCl are presented, and simulations of various lasing results are shown in the context of explicating dominant processes. Major kinetics issues are examined, particularly those leading to the model's rates for vibrational excitation of HCl and for electron quenching of the excited excimer molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343639
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  • 3
    Electronic Resource
    Electronic Resource
    Collisionally cooled spectroscopy: Pressure broadening below 5 K (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 122-125 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: New results from pressure broadening measurements between 4.3 and 1.7 K for the J=2←1 and 3←2 transitions of CO broadened by helium are reported. Unlike the results of helium pressure broadening experiments at higher temperature, significant variations in cross section occur with changes in temperature. These measurements are compared with the results of close coupling calculations and show both the effects of resonances in the collision channels and energy defects at the very low collision energies. Room-temperature measurements of helium pressure broadening have also been made on CO, NO, CH3F, and H2S. These provide a normalization for our previous studies of these species at very low temperatures and a basis for the qualitative comparison of the diverse results we have obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457498
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  • 4
    Electronic Resource
    Electronic Resource
    High pressure Raman study of the CO stretching mode in liquid N,N-dimethylacetamide (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4144-4149 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Raman ν4 symmetric C=O stretching mode of N,N-dimethylacetamide (DMA) is reported as a function of pressure from 1 to 4000 bar within the temperature range 40 to 100 °C. As in acetone, the isotropic line width ω1/2 (ISO) decreases with increasing density, in contrast to the opposite trend usually found in other molecular liquids. The noncoincidence effect, δω, which is the frequency difference between the peak maxima of the isotropic and the anisotropic Raman bands, increases with increasing density. These trends indicate the presence of strong intermolecular dipolar interactions between DMA molecules. Two theories of the noncoincidence effect due to McHale and Logan are used to interpret the density dependence of δω for DMA. In addition, we also used these two theoretical models to calculate δω for acetone using the results obtained earlier in our laboratory. McHale's theory can predict the correct density dependence for the noncoincidence effect when the dielectric screening factor is ignored. Logan's theory can account for the density behavior of the noncoincidence effect in DMA and in acetone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455772
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  • 5
    Electronic Resource
    Electronic Resource
    Kinetics of a structural phase transition in Langmuir monolayers studied using x-ray diffraction (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2393-2397 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Frequently, time-dependent effects are seen in monolayers of amphiphilic molecules (Langmuir films) when they are compressed, so that the pressure after some time is different from that recorded immediately after compression. We have identified for the first time a microscopic relaxation mechanism in monolayers of heneicosanol (C21H43OH): namely, a transition from a uniaxially distorted ("pseudohexagonal'') structural, formed upon compression, to an undistorted hexagonal structure. For T〉20 °C we observe only an apparently hexagonal phase, while at T=5 °C we observe only an apparently stable pseudohexagonal phase. When 10≤T≤20 °C, the monolayer structure changes with time from pseudohexagonal to hexagonal. The rate at which this transformation occurs is strongly temperature dependent. We propose that the observed temperature dependence is determined by the rate of nucleation of a hexagonal phase from a metastable shear-induced structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456653
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  • 6
    Electronic Resource
    Electronic Resource
    The effects of bending and stretching vibration on the reaction of acetylene cations with methane (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1577-1587 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multiphoton ionization (MPI) has been used to create C2H+2 in selected vibrational states, with excitation in either ν2 (C–C stretch) or a bending vibration (ν5-cis bend). Reactions of the state selected ions with CH4 and CD4 have been studied in a guided beam mass spectrometer. Absolute cross sections for formation of C3H+n (n=3,4,5) and C2H+3 products are reported for collision energies ranging from 60 meV to 5 eV. Evidence for both complex formation and direct reaction mechanisms is found. Vibrational excitation has different effects on the various product cross sections in different collision energy regimes. Bending excitation has also been found to cause somewhat different effects than C–C stretching vibration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456050
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  • 7
    Electronic Resource
    Electronic Resource
    The quantum mechanics of cluster melting (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 5651-5656 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present here prototype studies of the effects of quantum mechanics on the melting of clusters. Using equilibrium path integral methods, we examine the melting transition for small rare gas clusters. Argon and neon clusters are considered. We find the quantum-mechanical effects on the melting and coexistence properties of small neon clusters to be appreciable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456687
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  • 8
    Electronic Resource
    Electronic Resource
    On the resolution of an apparent conflict in the relation between position and momentum operators within the Hartree–Fock approximation (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5856-5857 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Time-dependent Hartree–Fock theory leads to two apparently quite different expressions relating matrix elements of the electronic position and momentum operators, depending upon whether a single-particle or a many-particle matrix element is used as the starting point. The two expressions are shown to be equivalent, in a complete Hartree–Fock basis set, by means of explicit use of the commutation properties of r with V and J on the one hand, and self-consistency relations and Brillouin's theorem on the other.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457539
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  • 9
    Electronic Resource
    Electronic Resource
    A model for impulsive mode–mode energy transfer in highly vibrationally excited molecules (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4582-4593 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The classical dynamics of mode–mode vibrational energy transfer are investigated for a coupled Morse oscillator system by explicitly integrating Hamiltonian's equations in action–angle coordinates. This method permit the identification of specific oscillator phase relationships which dictate the extent and timing of large-scale, nonperiodic energy transfer; we term this "impulsive energy transfer.'' In previous classical trajectory studies, such impulsive events have been related to the dynamics of isomerization immediately prior to reaction. A qualitative understanding of the required phase relationships for impulsive energy transfer is gained via the Chirikov hindered rotor analysis, usually applied to resonant energy flow. The implications of the model are illustrated in a three mode isomerization system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456618
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  • 10
    Electronic Resource
    Electronic Resource
    Hydrogen bonding and the Raman noncoincidence effect (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4632-4633 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456605
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