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  • American Institute of Physics (AIP)  (29)
  • Elsevier  (29)
  • 2000-2004  (18)
  • 1995-1999  (40)
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  • 21
    Electronic Resource
    Electronic Resource
    Simple modeling of line-mixing effects in IR bands. II. Nonlinear molecules applications to O3 and CHClF2 (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2185-2191 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A simple semiempirical approach is developed in order to model the shape of infrared absorption bands. It is based on use of the strong collision model and of a classical representation of rotational levels. The absorption coefficient then has a simple analytical expression whose wavenumber and pressure dependencies are computed by using eleven parameters which depend on the considered vibrational transition, the temperature, and the nature of the perturber only. These quantities, which are band-averaged values of the detailed spectroscopic and collisional parameters of the molecular system, can be deduced from direct fits of measured spectra. The model thus requires no previous knowledge of the characteristics of the molecules and is thus applicable to complex systems; in particular it seems a promising approach for very dense molecular spectra for which only absorption cross sections are now available. Tests are presented in the case of O3 and CHClF2 bands perturbed by N2 at room temperature for which new measurements have been made. They demonstrate the accuracy of our semiempirical approach in predicting the spectral shape in a wide range of density provided that effective parameters are used. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470974
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  • 22
    Electronic Resource
    Electronic Resource
    Line-mixing effects in N2O Q branches: Model, laboratory, and atmospheric spectra (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 1959-1968 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model based on the energy corrected sudden approximation is used in order to account for line-mixing effects in N2O Q branches of Σ↔Π bands. The performance of this theoretical approach is demonstrated by comparisons with many (about 70) N2O–N2 and N2O–O2 laboratory spectra recorded in the 5 and 17 μm regions by three instrument setups; the Q branches of the 2ν20e–ν21f (near 579.3 cm−1), ν2 (near 588.8 cm−1), and ν2+ν3 (near 2798.3 cm−1) bands are investigated for different pressures (0.1–2.0 atm) and temperatures (200–300 K). The model is used to generate a set of line-mixing parameters for the calculation of the absorption by the ν2 Q branch under atmospheric conditions. These data are tested by comparisons between computed stratospheric emissions and values measured using a balloon-borne high resolution Fourier transform instrument. The results confirm the need to account for the effects of line mixing and demonstrate the capability of the model to represent the N2O absorption in a region which can be used for the retrieval of N2O5 mixing ratios. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477862
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  • 23
    Electronic Resource
    Electronic Resource
    Temperature, pressure, and perturber dependencies of line-mixing effects in CO2 infrared spectra. III. Second order rotational angular momentum relaxation and Coriolis effects in Π←Σ bands (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7733-7744 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The energy corrected sudden approach is used in order to deduce collisional parameters and to model infrared quantities in Π←Σ bands of CO2–He and CO2–Ar mixtures in the 200–300 K temperature range. Measured line-broadening coefficients and absorption in the Q-branch of the ν2 band at moderate pressure are first used for the determination (from a fit) of the time constant associated with the relaxation of the second order traceless tensor of the rotational angular momentum (all other collisional quantities have been determined previously). The results obtained are consistent with previous (calculated) temperature dependent values of the depolarized Rayleigh cross sections. The model is then successfully tested through computations of absorption in the ν2 and (ν1+ν2)I bands at elevated densities. Analysis of line-mixing effects is made, including study of the influence of interbranch transfers and of Coriolis coupling. Differences between the effects of collisions with He and Ar are pointed out and explained. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478723
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  • 24
    Electronic Resource
    Electronic Resource
    Line-mixing effects in He- and N2-broadened Σ↔Π infrared Q branches of N2O (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6684-6690 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two Q branches of N2O near 579.3 and 2798 cm−1 belonging to the 2ν20e−ν21f and ν2+ν3 bands, respectively, of Σ←Π and Π←Σ symmetry, have been studied for He and N2 perturbers at pressures ranging from 0.1 to 2 atm, using a tunable diode laser and a difference-frequency laser spectrometer. To interpret the line-mixing effects in these spectra, we have applied a model based on the energy corrected sudden approximation whose parameters have been only derived from line-broadening data for N2O–He and also from the measured absorption by the Q branches for N2O–N2. This model provides a satisfactory agreement with experimental band shapes, whatever the band, the perturber and the pressure considered. Significantly larger line-mixing effects are shown for N2O–He with respect to N2O–N2. Finally, the assumption made in the calculations to treat separately the couplings in the even and odd j levels appears to have a negligible influence on the resulting band shapes. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477318
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  • 25
    Electronic Resource
    Electronic Resource
    Line mixing in the ν1 and 2ν2 isotropic Raman Q-branch of CO2 perturbed by argon and helium (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9315-9324 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The shapes of the ν1 and 2ν2 isotropic Raman Q-branch of CO2 perturbed by argon and helium have been measured by Stimulated Raman Spectroscopy (SRS) or coherent anti-Stokes Raman Spectroscopy (CARS) techniques. The data have been successfully analyzed with an energy corrected sudden (ECS) approximation model based on basic rates determined independently. Finally comparison of the present data with time resolved double resonance experiments allows us to discuss the physical origin of the two empirical constants which account for the shift and broadening of the branch due to vibrational effects. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480031
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  • 26
    Electronic Resource
    Electronic Resource
    Experimental and theoretical study of line mixing in methane spectra. III. The Q branch of the Raman ν1 band (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 1335-1343 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The shape of the ν1 Raman Q branch of CH4 perturbed by Ar and He at room temperature has been studied. Stimulated Raman spectroscopy (SRS) experiments have been made in the 2915–2918 cm−1 spectral region for total pressures from 0.4 to 70 atm and mixtures of (approximate)5% CH4 with He and Ar. Analysis of the spectra demonstrates that the shape of the Q branch is significantly influenced by line mixing and much narrower than what is predicted by the addition of individual line profiles. For the first time, a model is proposed for the calculation and analysis of the effects of collisions on the considered spectra. In this approach, the rotational part of the relaxation matrix is constructed, with no adjustable parameter, starting from semiclassical state-to-state rates. Two empirical constants which account for the shift and broadening of the branch due to vibrational effects are introduced and their values are determined from fits of measured spectra. Comparisons between measurements and results computed with and without the inclusion of line mixing are made. Although not perfect, our model satisfactory accounts for most effects of pressure at low densities, where rotational transfers are dominant, as well as at high densities, where the profile is strongly influenced by vibrational contributions. It is shown that collisions with He and Ar lead to different behaviors at elevated pressure. The influence of the perturbation introduced by the Fermi coupling between the ν1 and ν2+ν4 levels is discussed and the rotational and vibrational contributions to the spectral shape are pointed out. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480597
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  • 27
    Electronic Resource
    Electronic Resource
    Experimental and theoretical study of line mixing in methane spectra. II. Influence of the collision partner (He and Ar) in the v3 IR band (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 6850-6863 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Line mixing effects are studied in the v3 band of CH4 perturbed by Ar and He at room temperature. Experiments have been made in the 2800–3200 cm−1 spectral region using four different setups. They cover a wide range of total densities, including low (0.25–2 atm), medium (25–100 atm), and high (200–1000 atm) pressure conditions. Analysis of the spectra demonstrates that the spectral shapes (of the band, the Q branch, the P and R manifolds,...) are significantly influenced by line mixing. The theoretical approach proposed in the preceding paper is used in order to model and analyze these effects. As done previously, semiclassical state-to-state rates are used together with a few empirical constants. Comparisons between measurements and spectra computed with and without the inclusion of line mixing are made. They prove the quality of the approach which satisfactorily accounts for the effects of pressure and of rotational quantum numbers on the spectral shape. It is shown that collisions with He and Ar lead to different line-coupling schemes (e.g., more coupling within the branches and less between branches) and hence to different shapes. The influence of line coupling between different branches and manifolds is evidenced and studied using high pressure spectra and absorption in the band wings. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480095
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  • 28
    Electronic Resource
    Electronic Resource
    The CO oxidation kinetics on supported Pd model catalysts: A molecular beam/in situ time-resolved infrared reflection absorption spectroscopy study (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 4669-4684 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Combining molecular beam techniques and time-resolved infrared reflection absorption spectroscopy (TR-IRAS) we have studied the kinetics of the CO oxidation reaction on an alumina-supported Pd model catalyst. The Pd particles are deposited by metal evaporation under ultrahigh vacuum (UHV) conditions onto a well-ordered alumina film, prepared on a NiAl(110) single crystal. Particle size, density and structure of the Pd deposits have been characterized in previous studies. In the low temperature region, transient and steady-state experiments have been performed over a wide range of CO and oxygen fluxes by crossing two effusive molecular beams on the sample surface. We determine the steady-state CO2 production rate as a function of the CO fraction in the impinging gas flux. Simultaneously, the occupation of CO adsorption sites under steady-state conditions is monitored by in situ IR spectroscopy. The origin of different types of CO2 transients is discussed. In particular we focus on the transient CO2 production after switching off the CO beam. For the model catalyst investigated, detailed reaction rate measurements in combination with time-resolved IRAS show that the origin of the particular transient behavior of the supported model system is not due to the presence of specific adsorption sites on small particles, as has been proposed previously. Instead, we show that the transient behavior can be semiquantitatively simulated on the basis of a simple kinetic model considering a homogeneous surface, and accounting for the inhibition of the dissociative adsorption of O2 at high CO coverage. Moreover, it is discussed how the inherent heterogeneity of the supported particle system can additionally enhance the observed effect. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1342240
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  • 29
    Electronic Resource
    Electronic Resource
    Collision-induced absorption in the ν2 fundamental band of CH4. II. Dependence on the perturber gas (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 123-127 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The integrated intensities of the collision-induced enhancement spectra of the ν2 band of CH4 perturbed by rare gases and linear molecules (N2, H2, and CO2) are calculated theoretically using the quadrupole transition moment obtained from an analysis of CH4–Ar spectra. In addition to the isotropic quadrupole mechanism responsible for the enhancement in CH4-rare gases, there is additional absorption arising from the anisotropic quadrupole mechanism in the case of molecular perturbers. This latter effect involves the matrix element of the anisotropic polarizability for the ν2 transition in CH4 that is available from the analysis of the depolarized Raman intensity measurements. Overall, the theoretical values for the slope of the enhancement spectra with respect to the perturber density are in reasonably good agreement with the experimental results, thus confirming that the collision-induced absorption arises primarily through the quadrupolar induction mechanism. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1424311
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  • 30
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    Homogeneity measurements of plasma immersion ion-implanted complex-shaped samples (1997)
    Elsevier
    Details
    Publication Date: 1997-05-01
    Print ISSN: 0168-583X
    Electronic ISSN: 1872-9584
    Topics: Physics
    Published by Elsevier
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