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John P. Burrows - One of the best experts on this subject based on the ideXlab platform.

  • Application of a Gaussian Distribution Function To Describe Molecular UV−Visible Absorption Continua. 2. The UV Spectra of RO2• Radicals
    The Journal of Physical Chemistry A, 1997
    Co-Authors: D. Maric, John N. Crowley, John P. Burrows
    Abstract:

    The suitability of Gaussian Distribution Functions to describe the shape and temperature dependence of the UV absorption continua of peroxy radicals has been investigated. The ethylperoxy radical was used as a test case. Its 298 K absorption continuum was found to be best described by a semilogarithmic Gaussian Distribution Function. A linear Gaussian Distribution Function performed less well but still adequately described the continuous absorption. The temperature dependence of the ethylperoxy radical UV absorption continuum was also well predicted. Analogous results obtained for the methylperoxy radical support these conclusions. A theoretical comparison of the semilogarithmic and linear Gaussian Distribution Functions is given and a potential energy diagram of the ethylperoxy radical derived. The experimentally determined absorption cross sections of HO2• have been reanalyzed. It is shown that either the measurements at short wavelengths are in error or an unidentified electronic transition of HO2• exists.

  • Application of a Gaussian Distribution Function To Describe Molecular UV−Visible Absorption Continua. 1. Theory
    The Journal of Physical Chemistry, 1996
    Co-Authors: D. Maric, John P. Burrows
    Abstract:

    A number of mathematical descriptions of UV−visible absorption continua have been compared and contrasted by using some accurate measurements of the spectra of Cl2 and BrCl recorded at 298 K. The ability of such descriptions to accurately represent the absorption, their use in deconvolution, interpolation, and extrapolation was a focus of interest. The best description of continua was found to be that obtained using semilogarithmic Gaussian Distribution Functions. In addition, a quantum-mechanical approach based on spectral moments was developed in a novel manner as a convenient means to analyze the fitted continua and to compute their temperature dependence. The so-called “reflection method”, which has hitherto successfully been used for this purpose, was critically reanalyzed and its theoretical basis investigated. It was shown that, when correctly applied and interpreted, the reflection method yields a sufficiently accurate description of the temperature dependence of the UV−visible absorption continua...

  • A study of the UV—visible absorption spectra of Br2 and BrCl
    Journal of Photochemistry and Photobiology A: Chemistry, 1994
    Co-Authors: D. Maric, John P. Burrows, Geert K. Moortgat
    Abstract:

    Abstract A mathematical representation of the UV—visible absorption spectrum of Br 2 vapour, which is based on a four-band semi-logarithmic Gaussian Distribution Function, was derived in an assessment of the literature spectra where tanhtanh( hc ×325.3213 cm −1 /2 kT and λ is the wavelength in vacuum (200⩽λ⩽650 nm). The UV—visible absorption spectrum of BrCl (200⩽λ⩽600 nm) and the equilibrium coefficient for the reaction (Br 2 ) g + (Cl 2 ) g ← K BrCl → 2(BrCl) g were obtained by analysis of the absorption spectra of gaseous mixtures of Cl 2 and Br 2 , which were investigated at 298 K with a spectral resolution of 0.2 nm. The absorption cross-sections of BrCl are in good agreement with those reported by other workers and can be adequately described by a three-band semi-logarithmic Gaussian Distribution Function where tanhtanh( hc ×443.1 cm −1 /2 kT ) and λ is the wavelength in vaccum (200⩽λ⩽600 nm). In contrast with the spectrum of Br 2 vapour, no evidence was found for a fourth band in the spectrum of BrCl in the wavelength range studied. The value obtained for the equilibrium coefficient K BrCl (298 K)[BrCl] 2 /([Br 2 ][Cl 2 ]) = 10.1±1.1 is the largest reported so far. This yields a standard enthalpy for the formation of BrCl of Δ H BrCl °(298 K) = 14 307 J mol −1 .

D. Maric - One of the best experts on this subject based on the ideXlab platform.

  • Application of a Gaussian Distribution Function To Describe Molecular UV−Visible Absorption Continua. 2. The UV Spectra of RO2• Radicals
    The Journal of Physical Chemistry A, 1997
    Co-Authors: D. Maric, John N. Crowley, John P. Burrows
    Abstract:

    The suitability of Gaussian Distribution Functions to describe the shape and temperature dependence of the UV absorption continua of peroxy radicals has been investigated. The ethylperoxy radical was used as a test case. Its 298 K absorption continuum was found to be best described by a semilogarithmic Gaussian Distribution Function. A linear Gaussian Distribution Function performed less well but still adequately described the continuous absorption. The temperature dependence of the ethylperoxy radical UV absorption continuum was also well predicted. Analogous results obtained for the methylperoxy radical support these conclusions. A theoretical comparison of the semilogarithmic and linear Gaussian Distribution Functions is given and a potential energy diagram of the ethylperoxy radical derived. The experimentally determined absorption cross sections of HO2• have been reanalyzed. It is shown that either the measurements at short wavelengths are in error or an unidentified electronic transition of HO2• exists.

  • Application of a Gaussian Distribution Function To Describe Molecular UV−Visible Absorption Continua. 1. Theory
    The Journal of Physical Chemistry, 1996
    Co-Authors: D. Maric, John P. Burrows
    Abstract:

    A number of mathematical descriptions of UV−visible absorption continua have been compared and contrasted by using some accurate measurements of the spectra of Cl2 and BrCl recorded at 298 K. The ability of such descriptions to accurately represent the absorption, their use in deconvolution, interpolation, and extrapolation was a focus of interest. The best description of continua was found to be that obtained using semilogarithmic Gaussian Distribution Functions. In addition, a quantum-mechanical approach based on spectral moments was developed in a novel manner as a convenient means to analyze the fitted continua and to compute their temperature dependence. The so-called “reflection method”, which has hitherto successfully been used for this purpose, was critically reanalyzed and its theoretical basis investigated. It was shown that, when correctly applied and interpreted, the reflection method yields a sufficiently accurate description of the temperature dependence of the UV−visible absorption continua...

  • A study of the UV—visible absorption spectra of Br2 and BrCl
    Journal of Photochemistry and Photobiology A: Chemistry, 1994
    Co-Authors: D. Maric, John P. Burrows, Geert K. Moortgat
    Abstract:

    Abstract A mathematical representation of the UV—visible absorption spectrum of Br 2 vapour, which is based on a four-band semi-logarithmic Gaussian Distribution Function, was derived in an assessment of the literature spectra where tanhtanh( hc ×325.3213 cm −1 /2 kT and λ is the wavelength in vacuum (200⩽λ⩽650 nm). The UV—visible absorption spectrum of BrCl (200⩽λ⩽600 nm) and the equilibrium coefficient for the reaction (Br 2 ) g + (Cl 2 ) g ← K BrCl → 2(BrCl) g were obtained by analysis of the absorption spectra of gaseous mixtures of Cl 2 and Br 2 , which were investigated at 298 K with a spectral resolution of 0.2 nm. The absorption cross-sections of BrCl are in good agreement with those reported by other workers and can be adequately described by a three-band semi-logarithmic Gaussian Distribution Function where tanhtanh( hc ×443.1 cm −1 /2 kT ) and λ is the wavelength in vaccum (200⩽λ⩽600 nm). In contrast with the spectrum of Br 2 vapour, no evidence was found for a fourth band in the spectrum of BrCl in the wavelength range studied. The value obtained for the equilibrium coefficient K BrCl (298 K)[BrCl] 2 /([Br 2 ][Cl 2 ]) = 10.1±1.1 is the largest reported so far. This yields a standard enthalpy for the formation of BrCl of Δ H BrCl °(298 K) = 14 307 J mol −1 .

Geert K. Moortgat - One of the best experts on this subject based on the ideXlab platform.

  • A study of the UV—visible absorption spectra of Br2 and BrCl
    Journal of Photochemistry and Photobiology A: Chemistry, 1994
    Co-Authors: D. Maric, John P. Burrows, Geert K. Moortgat
    Abstract:

    Abstract A mathematical representation of the UV—visible absorption spectrum of Br 2 vapour, which is based on a four-band semi-logarithmic Gaussian Distribution Function, was derived in an assessment of the literature spectra where tanhtanh( hc ×325.3213 cm −1 /2 kT and λ is the wavelength in vacuum (200⩽λ⩽650 nm). The UV—visible absorption spectrum of BrCl (200⩽λ⩽600 nm) and the equilibrium coefficient for the reaction (Br 2 ) g + (Cl 2 ) g ← K BrCl → 2(BrCl) g were obtained by analysis of the absorption spectra of gaseous mixtures of Cl 2 and Br 2 , which were investigated at 298 K with a spectral resolution of 0.2 nm. The absorption cross-sections of BrCl are in good agreement with those reported by other workers and can be adequately described by a three-band semi-logarithmic Gaussian Distribution Function where tanhtanh( hc ×443.1 cm −1 /2 kT ) and λ is the wavelength in vaccum (200⩽λ⩽600 nm). In contrast with the spectrum of Br 2 vapour, no evidence was found for a fourth band in the spectrum of BrCl in the wavelength range studied. The value obtained for the equilibrium coefficient K BrCl (298 K)[BrCl] 2 /([Br 2 ][Cl 2 ]) = 10.1±1.1 is the largest reported so far. This yields a standard enthalpy for the formation of BrCl of Δ H BrCl °(298 K) = 14 307 J mol −1 .

Paola De Michelis - One of the best experts on this subject based on the ideXlab platform.

  • Non‐Gaussian Distribution Function of AE‐index fluctuations: Evidence for time intermittency
    Geophysical Research Letters, 1998
    Co-Authors: Giuseppe Consolini, Paola De Michelis
    Abstract:

    The probability Distribution Functions (Pdfs) of the AE-index fluctuations at different time scales have been investigated using a time series covering a period from January 01, 1978 to December 31, 1985. The Pdfs are always non Gaussian for time scales in the range 1–120 min both in quiet and disturbed periods. The scale dependence of the Pdfs indicates that AE-index is not characterized by a global time self-similarity, indicating that an intermittency phenomenon characterizes both phases. The results on Pdfs are compared with Functional form, proposed by Castaing et al. [1990], to characterize intermittency phenomena in ordinary turbulent fluid flows. Moreover the relevance of these observations to the understanding of the magnetospheric dynamical configuration is pointed out.

  • non Gaussian Distribution Function of ae index fluctuations evidence for time intermittency
    Geophysical Research Letters, 1998
    Co-Authors: Giuseppe Consolini, Paola De Michelis
    Abstract:

    The probability Distribution Functions (Pdfs) of the AE-index fluctuations at different time scales have been investigated using a time series covering a period from January 01, 1978 to December 31, 1985. The Pdfs are always non Gaussian for time scales in the range 1–120 min both in quiet and disturbed periods. The scale dependence of the Pdfs indicates that AE-index is not characterized by a global time self-similarity, indicating that an intermittency phenomenon characterizes both phases. The results on Pdfs are compared with Functional form, proposed by Castaing et al. [1990], to characterize intermittency phenomena in ordinary turbulent fluid flows. Moreover the relevance of these observations to the understanding of the magnetospheric dynamical configuration is pointed out.

J. K. Baird - One of the best experts on this subject based on the ideXlab platform.