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Line mixing effects in solar occultation



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Line mixing effects in solar occultation spectra of the lower stratosphere measurements and comparisons with calculations for the 1932 cm 1 CO2 branch Curtis P Rinsland and L Larrabee Strow Line mixing effects have been observed in a CO 2 Q branch recorded in 0 01 cm 1 resolution IR solar occultation spectra of the lower stratosphere The spectral data were obtained by the Atmospheric Trace MoleculeSpectroscopy Fourier transform spectrometer during the Spacelab 3 shuttle missionin the spring of 1985 Analysis of the 1932 47 cm 11102 00001 band Q branch ofl 2Cl 6 0 2 shows absorption coefficients below the band origin 0 62 times those calculated using a standard Voigt line shape function Calculations of line mixing using the Lorentz halfwidths of the lines and a simple energy gap scaling law to parametrize rotational energy transfer reproduce the observed absorption coefficients to 10 The present results provide the first quantitative information on air broadened line mixing effects in a Q branch at low temperatures 210 K and show that these effects are significant even at the low pressures of the lower stratosphere 100 mbar I Introduction A wide variety of remote sounding experiments utilize measurements of infrared vibration rotation bands to deduce atmospheric parameters such as pressure temperature and atmospheric composition In the inversion of the data the assumption is usually made that the absorption or emission can be calculated by summing the contributions of isolated Voigtshaped lines Although this assumption is satisfactory for many studies laboratory investigations have shownthat significant deviations from the Voigt shape occur in the infrared see for example Refs 1 3 One of the mechanisms that can produce deviations is interference effects caused by the overlapping of lines These interference effects often termed line mixing or coupling are predicted to be important in the far wings of lines 4 5 and in Q branches where the line spacing is small 6 7 Q



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