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  • 1
    Electronic Resource
    Electronic Resource
    Pseudolocal modes of guest molecules in mixed molecular crystals: Photon echo experiments and computer simulations (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3323-3334 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The temperature-dependent optical dephasing of anthracene, 9-methylanthracene, and 2-methylanthracene monomers in phenanthrene host crystals has been measured using photon echo experiments. Despite large linear electron–acoustic phonon coupling, all three systems dephase because of coupling to pseudolocal modes (local motions of the guest molecule). Computer simulations of the three systems calculate the pseudolocal mode eigenvalues and eigenvectors. In contrast to previous discussions in the literature which describe pseudolocal modes as librations, the predicted eigenvalues are in reasonable agreement with the measured pseudolocal mode energies. The predicted eigenvectors are combinations of translational motion along the long molecular axis and rotational motion about the out-of-plane axis of the guest. Differences in site energies for various locations and orientations of the methyl group are calculated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457844
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  • 2
    Electronic Resource
    Electronic Resource
    The A˜ 2Π–X˜ 2Σ+ transition of HC2 isolated in solid argon (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 3134-3142 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fourier transform absorption spectra have been obtained between 700 and 7900 cm−1 at a resolution of 0.2 cm−1 for Ar:C2H2 samples codeposited at 12 K with a beam of argon atoms that had been excited in a microwave discharge. Detailed isotopic substitution studies have confirmed that the predominant product species is HC2, which contributes not only the absorptions previously assigned to its two stretching fundamentals but also several weaker absorptions in the 2000–3600 cm−1 spectral region and a prominent, complicated pattern of absorptions between 3600 and 7800 cm−1. The previous assignment of the 3611 cm−1 HC2 absorption as the CH-stretching fundamental is reviewed, and the assignment of an absorption at 2104 cm−1 as ν2+ν3 of ground-state HC2 is discussed. The near infrared absorption band system has been assigned to the A˜ 2Π–X˜ 2Σ+ transition of HC2, extensively perturbed by interaction with high vibrational levels of the ground state. The position of the transition origin could not be definitively established. The previous assignment of gas-phase absorptions of HC2 at 3786, 4012, and 4108 cm−1 to ground-state combination bands has been confirmed, and carbon-isotopic data have been obtained for these bands. Because all of the HC2 absorptions observed in an argon matrix must originate in the X˜(000) state and because the observed matrix shifts are relatively small, these studies may provide a map to facilitate more detailed gas-phase studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452024
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  • 3
    Electronic Resource
    Electronic Resource
    Infrared spectrum of sodium hydride (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 6887-6892 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The infrared spectrum of gaseous NaH from 886 to 1245 cm−1 has been measured with a resolution of 0.015 cm−1 at temperatures between 670 to 720 °C. The v=1←0, 2←1, and 3←2 transitions have been observed and combined with rotational transitions measured by others to obtain appropriate rovibrational constants and Dunham potential constants. The Herman–Wallis intensity effect has been measured in order to estimate a transition moment of 0.31±0.05 D for the v=1←0 transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456263
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  • 4
    Electronic Resource
    Electronic Resource
    Infrared spectrum of the overtone band 2ν05 of the hydrogen bonded complex HCN---HF (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2401-2405 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The infrared spectrum of the overtone of the "intramolecular'' bending vibration 2ν05 of the hydrogen bonded complex HCN---HF centered at 1437.539 91(24) cm−1 has been obtained with a resolution of 0.006 cm−1. Line assignments for this band as well as two hot bands 2ν05+ν17−ν17 and 2ν05 +2ν27−2ν27 have been made, and rotational constants for all the levels involved have been determined. Despite the fact that the higher J energy levels of the observed lines of 2ν05 are above the dissociation energy of the complex, no predissociative line broadening is apparent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451095
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  • 5
    Electronic Resource
    Electronic Resource
    Instrument to measure the polarization state of waves (1985)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 56 (1985), S. 278-282 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We report here on the design and implementation of analog circuitry which allows the processing of the components of vector waveforms to obtain polarization information. The waveforms are the voltages derived from orthogonal sensors such as magnetometers or seismometers which provide information on the time variation of vector processes. The circuits take the voltages from the individual sensors and process them to produce estimates of the spectral matrix at a particular frequency. From the components of the spectral matrix one may determine the wave polarization parameters including the signal power, ellipticity, handedness, and orientation of the polarization ellipse. In cases where the information of interest to the investigator depends upon the relatively slow modulations of a carrier and not upon the frequency of the carrier itself, the preprocessing of the spectral information as described here allows the investigator to sample the data at a much reduced rate, or with a narrower bandwidth, without loss of information. We have implemented the circuits described in our investigation of electromagnetic waves in the ULF (3 mHz–3 Hz) frequency band and have achieved a reduced demand for storage and processing capacities in the project.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138344
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  • 6
    Electronic Resource
    Electronic Resource
    Theory of nonadiabatic gas–surface reactions (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1392-1403 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical description of near-resonant charge-exchange processes occurring in gas–surface collisions is presented. The diatomics in molecules method is used for the electronic description of a surface consisting of five atoms. The gas–surface interaction potentials and couplings are obtained with the polyatomics in molecules approach. Trajectories for the "nuclear'' variables and transition probabilities are calculated with the common eikonal formalism. Preliminary results are presented for Na scattering from a W(110) surface. The initial kinetic energy of the sodium atom is varied between 5 and 60 eV and its trajectory is restricted to be perpendicular to the surface and striking the center W atom. The results show a noticeable probability (≤20%) for electron transfer to the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449457
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamics of superionic conduction: A generalized Langevin equation study of mobile cation channeling and activated barrier crossing in α-AgI (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1865-1876 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: MTGLE and Langevin equation stochastic classical trajectory studies of the mobile silver cation channeling and activated barrier crossing processes which underly superionic conduction in α-AgI are presented. To interpret non-Kramers effects on the channeling kinetics, a new description of the condensed phase effect on activated barrier crossing is developed. This picture emphasizes the competition between "whipback'' of the reaction coordinate, arising from instantaneous environmental restoring forces, and frequency-dependent dissipation of reaction coordinate energy due to environmental relaxation. The simulations show that while the roughest features of the channeling trajectories are determined by the cation friction coefficient the finer details are governed by short-time scale cation-cage correlations. Analogously, for α-AgI, the gross features of the kinetics, e.g., the rough extent of the breakdown of the transition state model, are described by a Kramers-like picture. The finer details of the kinetics, however, are governed by the competition between whipback, which makes realistic barrier crossing less efficient than Kramers model barrier crossing, and dissipation, which works in the opposite direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449374
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  • 8
    Electronic Resource
    Electronic Resource
    Rovibrational analysis of ν3 HCN---HF using Fourier transform infrared spectroscopy (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 6188-6192 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The gas phase rovibrational spectrum of the ν3 band arising from the C≡N stretching vibration in the hydrogen bonded heterodimer HCN---HF has been observed at 0.004 cm−1 instrumental resolution using a Fourier transform infrared spectrophotometer. Analysis of the spectrum gave the following molecular parameters (in cm−1): ν3=2120.935(12), α3=+5.06(19)×10−4, B'=0.119 283(19), D'J=2.30(7)×10−7. Excited state amplitude lifetimes of observed transitions are demonstrated to be 5.6(4)×10−10 s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449564
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  • 9
    Electronic Resource
    Electronic Resource
    Equilibria and kinetics of polydisperse mixture adsorption (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 3868-3874 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the equilibrium and kinetic properties of a model for polydisperse mixture adsorption. The system consists of a bulk phase of hard disks with a given size distribution and overall concentration that adsorb and desorb on a continuous planar surface. The disks adsorb at a rate proportional to their bulk concentration and desorb at a rate that may depend on the particle size. The model is characterized by α, the dimensionless binding energy of a solute per unit area, and K which is proportional to the total bulk concentration. The properties of the model are determined with scaled particle theory (SPT) and with numerical simulation. If the desorption rate is independent of particle size, an equilibrium is rapidly established between the bulk and adsorbed phases. The resulting adsorption isotherms predicted by SPT agree well with the numerical simulations. If the desorption rate depends exponentially on the binding energy of the adsorbed particle, the approach to equilibrium is dramatically slowed. At high bulk concentrations and low values of α the adsorbed density increases monotonically with time, while the coverage displays an overshoot. At low K and high α, it is the coverage that increases monotonically, while the density passes through a maximim. For a given bulk phase distribution, one can construct an (α,K) kinetic phase diagram delineating this behavior. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480534
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  • 10
    Electronic Resource
    Electronic Resource
    The dependence of DNA tertiary structure on end conditions: Theory and implications for topological transitions (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 10990-10996 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Explicit expressions are derived for the equilibrium configurations of long segments of a DNA double helix subject to boundary conditions of the type imposed by DNA-bending proteins at the ends of otherwise free segments. The expressions, which are exact within the framework of Kirchhoff's theory of elastic rods, show that, in appropriate ranges of parameters, small changes in end conditions can result in large changes in tertiary structure. A discussion is given of the implications of this observation for understanding the action of bending proteins and of proteins that induce topological transitions that change the linking number of closed loops of DNA. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467849
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