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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 5567-5579 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theory is presented for the modification of the line-shape functions and absorption coefficient due to the breakdown of the quasistatic approximation. This breakdown arises from the effects of molecular motion and increases the absorption in the near wings. Numerical calculations for the high-frequency wing of the ν3 band of CO2 broadened by Ar are reported and it is shown that these effects are significant near the bandhead. The importance of such corrections in other spectral regions and for other systems is discussed briefly.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 6290-6301 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theory is presented for the calculation of the continuous absorption due to the far wing contributions of allowed lines. The theory is based on the quasistatic approximation for the far wing limit and the binary collision approximation of one absorber molecule and one bath molecule. In line space, the motion of the dipole moment of the absorber molecule, determined by the time displacement Liouville operator related to the total Hamiltonian of the absorber molecule and the bath molecule, is approximately expressed as the ordered product of two time displacement Liouville operators, one related to the intermolecular potential and the other to the unperturbed Hamiltonian. Using a Laplace transformation, the spectral density is expressed in terms of a Cauchy integral whose integrand is a product of two resolvent operators corresponding to the interaction and to the unperturbed Hamiltonian, respectively. After isolating the effects of the bath variables, the spectral density and subsequently the absorption coefficient are expressed in terms of the individual line coupling functions, or the individual line shape functions. By using two average line shape functions instead of the individual ones, the expression of the absorption coefficient closely matches empirical models. The validity of the present theory is discussed, and some numerical results of the water continuum absorption in the infrared region are presented for comparison with experimental data. A good agreement in both the magnitude and the temperature dependence of the absorption coefficients is obtained. Some further extensions and applications of the present theory are also discussed briefly.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 6127-6139 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theory is presented for the calculation of the continuous absorption of water molecules in the millimeter spectral region. The theory is based on a generalization of Fano's theory in which the spectral density, the Fourier transform of the dipole-moment correlation function, is calculated for a system consisting of a pair of molecules. The internal states are written in terms of the line space of the system, and the resolvent operator is obtained using the well-known Lanczos algorithm. For the interaction between two water molecules, we include only the leading dipole–dipole term of the long-range anisotropic potential, and model the isotropic interaction, used to calculate the statistical weight within the quasi-static approximation, by a Lennard–Jones potential. Using reasonable values for the two Lennard–Jones potential parameters, and the known rotational constants and permanent dipole moment of a water molecule, we calculate the absorption coefficient for frequencies up to 450 GHz for temperatures between 282 and 315 K. The present results are in good agreement with an empirical model for the water continuum based on combined laboratory and atmospheric measurements. We conclude from our results that, contrary to some previous assertions, the strong negative temperature dependence as well as the magnitude of the continuum absorption, at least for the millimeter spectral region, can be explained in terms of the far-wings of allowed rotational transitions.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 15 (1984), S. 38-40 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Accurate theoretical expressions for Herman-Wallis factors for the pure rotational, fundamental and first two overtone vibration-rotational bands have been derived. These are expressed for arbitrary rotational quantum numbers in terms of the Dunham potential parameters and the coefficients of a general operator represented by a power series expansion. The inclusion of higher order corrections in a consistent way reduces the discrepancy reported by previous workers for H2 between results obatined numerically and analytically. The present expressions are of sufficient accuracy to enable one to obtain precise experimental values for the anisotropy of the polarizability and its derivatives from an analysis of Raman line intensities.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3009-3010 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Comparisons are made between different methods of introducing the principle of detailed balance in far-wing line shape theories. In particular, it is shown that by symmetrizing the operators in the quasistatic formulation of Ma and Tipping [J. Chem. Phys. 95, 6290 (1991)], one can obtain the same results for the symmetrized matrix elements of the relaxation operator and their frequency detuning that were introduced in an ad hoc way in the resonant quasistatic formulations of Boulet and co-workers [J. Chem. Phys. 91, 2163 (1989); 94, 6406 (1991)]. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8720-8736 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The formalism developed previously for the calculation of the far-wing line shape function and the corresponding absorption coefficient using a single-component anisotropic interaction term and the binary collision and quasistatic approximations is generalized to multicomponent anisotropic potential functions. Explicit expressions are presented for several common cases, including the long-range dipole–dipole plus dipole–quadrupole interaction and a linear molecule interacting with a perturber atom. After determining the multicomponent functional representation for the interaction between CO2 and Ar from previous published data, we calculate the theoretical line shape function and the corresponding absorption due to the ν3 band of CO2 in the frequency region 2400–2580 cm−1 and compare our results with previous calculations carried out using a single-component anisotropic interaction, and with the results obtained assuming Lorentzian line shapes. The principal uncertainties in the present results, possible refinements of the theoretical formalism, and the applicability to other systems are discussed briefly.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1428-1428 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7066-7075 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The statistical theory proposed by Rosenkranz to calculate the continuous absorption by water molecules in the high-frequency (infrared) wing of the pure rotational band is reviewed and extended. In the review there is a discussion, in particular, of the approximations that are made, including those that are necessary and which limit the applicability of the theory to other spectral regions, and those that are made for calculational convenience. Then, several extensions to the theory are discussed, including increasing the number of rotational states used to calculate the band-average relaxation parameter, modifying the definition of this parameter to account for near-wing effects, and eliminating the boxcar approximation. This last modification, effected by using asymmetric-top functions instead of symmetric-top functions to calculate matrix elements of the density operator and to diagonalize the dipole–dipole interaction, results in significant enhancement of the relaxation parameter. This improvement, in turn, allows one to eliminate an inconsistency in the original formulation of Rosenkranz while obtaining substantially the same final results. The implications of the present results for the calculation of the absorption in the high-frequency wing of the ν2 fundamental vibration-rotational band of H2O are discussed briefly.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5505-5508 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Multidimensional harmonic oscillator matrix elements of arbitrary products of exponentials for operators containing only linear and quadratic terms in the creation and annihilation operators are obtained. A simple and straightforward method is presented that leads to recurrence relations and generating functions for such matrix elements. Results are shown to be general enough to cover the cases of Franck–Condon overlaps, transition probabilities for time-dependent harmonic oscillators, and correlation functions for electronic spectra.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 818-828 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The far wing line shape theory developed previously and applied to the calculation of the continuum absorption of pure water vapor is extended to foreign-broadened continua. Explicit results are given for H2O–N2 and H2O–CO2 in the frequency range from 0 to 10 000 cm−1. The theory is based on the quasistatic and binary collision approximations and assumes for the interaction potential an isotropic Lennard-Jones part and the leading anisotropic multipolar (dipole–quadrupole) term. For H2O–N2, the positive and negative resonant frequency average line shape functions and absorption coefficients are calculated for a number of temperatures between 296 and 430 K for comparison with existing laboratory data. In general, the agreement is very good, especially at the higher temperatures for which the experimental absorption is larger and the corresponding error limits are smaller. For H2O–CO2 for which no experimental data exists, the calculations are made only at 296 K. Because of the significantly different line shapes for self vs foreign broadening, the ratio of the corresponding continuum absorption coefficients varies widely as a function of the frequency. The implications of this for absorption in the Earth's atmosphere are discussed briefly.
    Type of Medium: Electronic Resource
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