Knowledge Bank

The water-vapor continuum and selective absorption in the atmospheric windows strongly affect the radiative balance of the Earth. We have previously reported preliminary experimental results on the water-vapor continuum absorption}$ International Symposium on Molecular Spectroscopy, Columbus (2006)} between 8 $\mu$m and 12.5 $\mu$m. About 200 spectra were recorded at 0.1 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$ resolution for six temperatures between 311 K and 363 K. The spectra were acquired at pathlengths from 76 m to 116 m using a 2 m long White cell coupled to a BOMEM DA8.002 FTIR spectrometer. Water-vapor pressures varied from 2.8 kPa (21 torr) to 15.1 kPa (113 torr). A special spectral processing program calculates, fits, and removes ro-vibrational structure from the spectrum. Regions freed from spectral structure were used to retrieve averaged and smoothed binary absorption coefficients between 8 $\mu$m to 12.5 $\mu$m and 4.5 $\mu$m to 5.2 $\mu$m. Our continuum data extrapolated to room temperature are in reasonable agreement with the CKD continuum model}, 229, (1989)}. However, at high temperatures the CKD model provides values up to 50$\%$ less than experimentally measured. While processing the spectra we have found that the intensities of several ro-vibrational lines in the HITRAN database need to be corrected. Also, at the relatively high vapor pressures mentioned above a self-induced pressure shift of several lines has been detected.