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  • 1
    Electronic Resource
    Electronic Resource
    Brillouin scattering and segmental motion in polystyrene-cyclohexane solutions (1982)
    s.l. : American Chemical Society
    Macromolecules 15 (1982), S. 557-561 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00230a068
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  • 2
    Electronic Resource
    Electronic Resource
    Optical pumping studies of vibrational energy transfer in high-pressure diatomic gases (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1178-1186 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spontaneous Raman scattering is used to experimentally determine the vibrational distribution functions of diatomic species in N2/CO and N2/CO/O2 gas mixtures optically pumped by a CO laser in the pressure range 410–760 torr. In N2/CO mixtures, as many as 38 vibrational levels of CO are observed, in addition to six levels of N2. The CO vibrational distribution function is highly non-Boltzmann, exhibiting the well-known Treanor plateau. In N2/CO/O2 mixtures, up to 13 vibrational levels of O2 are observed, which also exhibit a highly non-Boltzmann distribution. Experimental data are compared to predictions of a master equation kinetic model, which incorporates absorption of the laser radiation, species, and quantum state-specific vibration–vibration and vibration–translation energy exchange, as well as diffusion of vibrationally excited species out of the laser-excited volume. It is shown for the first time that modest power continuous wave lasers can be used to establish highly excited steady-state vibrational distributions of all three major diatomic species in CO-seeded atmospheric pressure dry air. This has implications for the energy-efficient creation of low-temperature, high-pressure air plasmas, in which the principal free electron loss mechanism is known to be three-body attachment to molecular oxygen. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1332400
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  • 3
    Electronic Resource
    Electronic Resource
    QUANTITATIVE FLOW VISUALIZATION IN UNSEEDED FLOWS (1997)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 29 (1997), S. 285-326 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The various tools for flow visualization have been significantly expanded over the past several years through the use of molecular scattering and molecular laser-induced fluorescence. These approaches have added the capability of sampling individual small volume elements within a flow, and by using cameras for detection, they are easily extended to sample lines and cross-sectional planes. This localized measurement capability means that these approaches can be made quantitative even in complex and/or unsteady flow fields. If the molecular species is naturally occurring, such as oxygen or nitrogen in air, then no seeding is required. Furthermore, in these applications, images of the flow can be frozen in time by using a short pulse laser for illumination. The distribution of the molecules reflects the true physics of the flow, so even raw images taken in this manner give an immediate understanding of flow field properties. With proper calibration, the images can be further analyzed to yield quantitative information about the flow. In the case of flow tagging, the analysis gives velocity profiles when lines are written, and deformation, vorticity, and dilation with grid patterns. Molecular scattering can be used to give quantitative values of density, temperature, and two-dimensional velocity. This paper presents three such molecular-based approaches: laser-induced fluorescence from oxygen, flow tagging by oxygen excitation, and Rayleigh scattering. These three approaches are chosen because all three can be used in naturally occurring air with no seeding. The raw data from each of these approaches gives an immediate appreciation of the flow structure and further analysis yields accurate values of velocity, temperature, and density. These approaches use readily available laser sources; however, they will be greatly enhanced with new source technologies that are currently under development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fluid.29.1.285
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  • 4
    Electronic Resource
    Electronic Resource
    Time domain modeling of spectral collapse in high density molecular gases (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 8299-8309 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In many cases, the widely used matrix inversion approach to describe the spectral interference in collisionally perturbed molecular spectra is not feasible if the particular molecular interactions do not allow the sudden impact approximation (infinitely short collision duration). To overcome this problem, we present a time domain model that describes collisional broadening and narrowing phenomena without requiring the sudden approximation. The key element of the model is a Monte Carlo type sampling process to quantify the temporal autocorrelation of the molecular dipole moment. The spectrum is then obtained numerically via fast Fourier transform. The model does not require a frequency-dependent relaxation operator; the finite collision duration is simply an adjustable parameter in the time domain process. Our approach, which is generally applicable to any set of transition lines, is derived from concepts of both conventional quantum-mechanical and semiclassical theory of line interference. Coherent transfer effects from rotationally inelastic collisions are described as randomly occurring events which affect frequency, amplitude, and phase of the sampled oscillation. Effects of vibrational dephasing are included as well. To demonstrate its feasibility, we apply the model here to the 2.7 μ absorption spectrum of carbon dioxide diluted in high density air (ρ=43–485 amagat, T=297–754 K). The successful modeling of the experimental data, especially the full collapse of P and R branches at ultrahigh densities, accounts for interbranch mixing and for incoherent effects. The calculations make extensive use of the new Hitran (HITEMP) molecular database. Results include revised estimates for the collision duration of CO2 with nitrogen and oxygen at room temperature. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473893
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  • 5
    Electronic Resource
    Electronic Resource
    Interbranch line-mixing in CO2 (1001) and (0201) combination bands (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 5995-6004 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Absorption spectra from a mixture of 320 ppm CO2 in synthetic air (79% N2, 21% O2) were collected in the region from 3500 cm−1 to 4000 cm−1 under conditions in the range of 100–1000 atm and 295–900 K. At 295 K, both bands of the (1001), (0201) Fermi dyad show the collapse of P and R branches into a single nearly Lorentzian spectral feature as a result of interbranch line-mixing. At elevated temperatures, the presence of interbranch mixing is also clearly evident as is the presence of several hot bands. The experimental data are modeled using two methods for simulating line-mixed spectra; first, the usual line-by-line approach which relies on the binary impact approximation, and second, a simple band-averaged model proposed by Hartmann and L'Haridon [J. Chem. Phys. 103, 6467 (1995)]. The energy corrected sudden (ECS) approximation is used to generate the relaxation matrix in the first approach. Comparison with the measurement shows that the ECS method does not fit the high density data satisfactorily when adjustable parameters from the literature are used; the level of interbranch mixing must be decreased by about a factor of 2 relative to intrabranch mixing and at least 5% dephasing must be added to the ECS matrix. With these changes, the room temperature data are modeled satisfactorily, but significant discrepancies are still present in the high temperature spectra. On the other hand, the simpler band-averaged model does provide a reasonable estimate of the spectra for all temperatures when best fit values are used for mixing and broadening, but the low density data are not reproduced as well as with the ECS model. Data from high pressure absorption measurements in a 1% NO in N2 mixture as well as a 0.5% CH4 in N2 mixture are also presented without analysis, showing the effects of interbranch line-mixing in these spectra. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474268
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  • 6
    Electronic Resource
    Electronic Resource
    Radio frequency energy coupling to high-pressure optically pumped nonequilibrium plasmas (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5911-5918 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article presents an experimental demonstration of a high-pressure unconditionally stable nonequilibrium molecular plasma sustained by a combination of a continuous wave CO laser and a sub-breakdown radio frequency (rf) electric field. The plasma is sustained in a CO/N2 mixture containing trace amounts of NO or O2 at pressures of P=0.4–1.2 atm. The initial ionization of the gases is produced by an associative ionization mechanism in collisions of two CO molecules excited to high vibrational levels by resonance absorption of the CO laser radiation with subsequent vibration-vibration (V-V) pumping. Further vibrational excitation of both CO and N2 is produced by free electrons heated by the applied rf field, which in turn produces additional ionization of these species by the associative ionization mechanism. In the present experiments, the reduced electric field, E/N, is sufficiently low to preclude field-induced electron impact ionization. Unconditional stability of the resultant cold molecular plasma is enabled by the negative feedback between gas heating and the associative ionization rate. Trace amounts of nitric oxide or oxygen added to the baseline CO/N2 gas mixture considerably reduce the electron–ion dissociative recombination rate and thereby significantly increase the initial electron density. This allows triggering of the rf power coupling to the vibrational energy modes of the gas mixture. Vibrational level populations of CO and N2 are monitored by infrared emission spectroscopy and spontaneous Raman spectroscopy. The experiments demonstrate that the use of a sub-breakdown rf field in addition to the CO laser allows an increase of the plasma volume by about an order of magnitude. Also, CO infrared emission spectra show that with the rf voltage turned on the number of vibrationally excited CO molecules along the line of sight increase by a factor of 3–7. Finally, spontaneous Raman spectra of N2 show that with the rf voltage the vibrational temperature of nitrogen increases by up to 30%. This novel energy efficient approach allows sustaining large-volume high-pressure molecular plasmas without the use of a high-power CO laser. This opens a possibility of using the present technique for high-yield plasma chemical synthesis and plasma material processing. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1359755
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