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A number of mathematical descriptions of UV-visible absorption continua have been compared and contrasted by using some accurate measurements of the spectra of Cl 2 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 for most applications in the fields of atmospheric and combustion chemistry. Furthermore, it is simpler and less computationally demanding than any other technique and is useful for obtaining the initial values needed for the iterative procedures inherent to the more accurate quantum-mechanical methods of spectral analysis. The semilogarithmic Gaussian distribution functions may also successfully be applied to the description of structured UV-visible spectra, provided that the detail of the structure is ignored.

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