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Absolute absorption coefficients of ClONO 2 infrared bands at stratospheric temperatures

1988; American Geophysical Union; Volume: 93; Issue: D2 Linguagem: Inglês

10.1029/jd093id02p01659

2156-2202

J. Ballard, W. B. Johnston, M. R. Gunson, Paul Wassell,

Atmospheric chemistry and aerosols

Fourier‐transform absorption spectroscopy has been used in the laboratory to obtain absolute absorption coefficients σ(ν) in infrared bands of ClONO 2 in the 700–1800 cm −1 spectral region. These data have been obtained over a temperature range (213–296 K) corresponding to stratospheric temperatures. The results are therefore applicable to retrievals of stratospheric ClONO 2 from remote‐sensing observations. Room temperature absorption coefficients are some 25% larger than previously reported values, and large temperature dependences in the absorption coefficients have been observed. The ν 1 and ν 2 bands behave as simple fundamentals of a system which has low‐energy vibrational or torsional modes, with little contribution from hot bands over the temperature range used. The intensity in the ν 2 Q branch increased by 53% over the temperature range 296–213 K. A similar increase was observed for the ν 4 Q branch, and significant hot‐band features were seen in the ν 3 , ν 4 spectral region. The ν 4 Q branch and the ν 2 Q branch were observed to obey the Beer‐Lambert law over the range of pressure, temperature, absorber amount, and resolution employed. The absorption coefficients in the ν 4 Q branch and in the ν 2 band were modeled by equispaced absorption lines, each characterized by a central frequency, strength, lower‐state energy, and pressure‐broadened width.