Accurate models are needed to represent both the local lines and the continuum absorption in spectral ranges of interest. Additionally, accurate experimental data are needed, under different conditions of pressure and temperature, to test the validity of various models. Experimental data are obtained from a BOMEM fourier transform spectrometer (FTS) with a high pressure-high temperature cell and a 10-m white cell. Absorption coefficients are determined for gas mixtures (H2O, CO2, N2, O2) for pressure up to 60 atm and temperatures up to 600 K. At high pressure, the Lorentzian approach fails, and semi- empirical models are used to represent local line and far wing phenomena. The far wing nature of the line shape theory of Birnbaum is used to represent the water vapor continuum. Comparisons are made between our experimental data and synthetic spectra based on the HITRAN data base and Birnbaum's line shape for several atmospheric transmission window regions. Implications concerning atmospheric propagation are emphasized
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Infrared absorption by the water vapor continuum near 1200 cm-1 has been measured with a lead-tin-telluride diode laser over a 40.5-m optical path. The measurements were made as a function of temperature from 333 K to 473 K; thus, they overlap and extend previous measurements made at temperatures between 293 K and 388 K. Over the entire temperature range studied here, the continuum extinction coefficient increases quadratically with water-vapor partial pressure as expected for the relatively high partial pressures used in these measurements. At temperatures below 398 K. our measured extinction coefficients agree well with previously reported data. At higher temperatures, however, the extinction coefficient is almost independent of temperature and is substantially larger than predicted by empirical formulas. Values of the self-broadening coefficient for water vapor have been extracted from the experimental data, and a possible interpretation of the results involving both dimer and line-broadening effects is presented.
