We report measurements of the water vapor continuum using infrared cavity ringdown spectroscopy at frequencies of 931.002, 944.195, and 969.104 cm−1. Our values of the water vapor continuum coefficients for self-broadening at T = 296K are Cs0 (931cm−1) = 2.23±0.17, Cs0(944cm−1) = 2.02±0.13, and Cs0(969cm−1) = 1.79±0.21×10−22molecules−1cm2atm−1. Our measurements are found to be in good agreement with the far wing line shape theory of Ma and Tipping, but we find that empirical models of the water vapor continuum, widely used in radiative transfer calculations, significantly overestimate the observed self-broadened continuum.
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In this paper we report the results of a series of pressure-broadened water vapor absorption measurements at 27 CO2 laser frequencies between 935 cm-1 and 1082 cm-1. Both multiple traversal cell and optoacoustic (spectrophone) techniques were utilized together with an electronically stabilized cw CO2 laser. Comparison of the results obtained by these two methods shows remarkable agreement, indicating a precision which has not been previously achieved in pressure-broadened studies of water vapor. The data of 10.59 Am substantiate the existence of the large (>200) self-broadening coefficients determined in an earlier study by McCoy. In this work we have treated the case of water vapor in N2 at a total pressure of 1 atm. We have also studied water vapor in air and will report those results separately.
