The continuum absorption in H2O+N2 mixtures in the 2000-3250 cm−1 spectral region at temperatures from 326 to 363 K

The absorption spectra of H2O+N2 mixtures, as well, as the spectra of pure gases, have been measured using a Fourier-transform infrared spectrometer at a resolution of 0.1 cm−1. The sample temperatures were 326, 339, 352, and 363 K. Water vapor pressures varied from 8 (60 torr) to 34.5 kPa (259 torr). The nitrogen pressure was kept constant at about 414 kPa (4.1 atm). The path length was 100 m. The continuum absorption coefficients obtained in the spectral range 2000-3250 cm−1 (3.1-5 μm) do not depend significantly on temperature, as is predicted by the well known MT_CKD model. But there are significant deviations in the continuum spectral behavior and magnitude. Around 2050 cm−1 the measured absorption coefficients Cf are about two times larger than those of the model. This deviation grows rapidly at shorter wave lengths, reaching a maximum of two orders of magnitude in the middle of the window at 2500 cm−1. At this point, the deviation starts to decrease significantly and around 3100 cm−1 our results are in agreement with the MT_CKD model. This behavior of the deviation is due to the broad and structureless feature in the region of the nitrogen fundamental band. Most likely, this feature is the N2 fundamental band component, induced by collisions between H2O and N2 molecules. The data obtained and a comparison with the results from the other available sources are presented.

► The continuum absorption in H2O+N2 mixtures in the 4 μm region is investigated. ► The data are compared with the other available data and with the continuum model. ► Disagreements are discussed.