Laser-photoacoustic spectroscopy of water-vapor continuum and line absorption in the 8 to 14-micron atmospheric window

Four weak absorption lines which occur at the CO2-laser emissions 10P(40), 10R(20), 9P(38) and 9R(36) have been assigned to pure rotational transitions of H2O, and the dependence of the continuum water-vapor absorption over the temperature range +70 to -20 C has been determined. The measured negativ...

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Bibliographic Details
Published in:Infrared physics 1987-03, Vol.27, p.63-120
Main Authors: HINDERLING, J, Sigrist, M W, Kneubuehl, F K
Format: Article
Language:English
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Summary:Four weak absorption lines which occur at the CO2-laser emissions 10P(40), 10R(20), 9P(38) and 9R(36) have been assigned to pure rotational transitions of H2O, and the dependence of the continuum water-vapor absorption over the temperature range +70 to -20 C has been determined. The measured negative temperature coefficient of the continuum is consistent with both monomer and dimer models, yet not with predictions of larger water clusters. Experiments with supersaturated water vapor indicate that for S equal to or greater than 1 collision broadening of distant strong lines as well as water dimer absorption contribute to the continuum. However, the dimer absorption is an order of magnitude too small to cause a significant contribution at ambient atmospheric conditions. The measured spectra have been compared with LOWTRAN 6 and HITRAN models. The LOWTRAN yields a stronger negative temperature dependence than observed while the HITRAN does not predict the observed continuum absorption. (Author)
ISSN:0020-0891