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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Water continuum CO2 laser absorption spectra are reported for temperatures between 27 and -10°C. The continuum is found to possess a negative temperature coefficient. The results obtained suggest that the magnitude of this temperature coefficient increases with increasing water pressure and decreasing temperature. The temperature coefficients between 27 and 10°C for air mixtures containing 3.0- and 7.5-Torr water vapor are -2.0 ± 0.4 and -2.9 d 0.5%/ C, respectively. For mixtures with 3.0-Torr water the 10-O°C temperature coefficient is -7.7 ± 0.2%/°C. The temperature and water pressure dependencies observed for the continuum suggest that while both collisional broadening and water dimer mechanisms contribute to the continuum, the dimer mechanism is more important over this temperature range.
