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Published August 14, 2011 | Published
Journal Article Open

The air-broadened, near-infrared CO_2 line shape in the spectrally isolated regime: Evidence of simultaneous Dicke narrowing and speed dependence


Frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) was employed to measure airbroadened CO_2 line shape parameters for transitions near 1.6 μm over a pressure range of 6.7–33 kPa. The high sensitivity of FS-CRDS allowed for the first measurements in this wavelength range of air-broadened line shape parameters on samples with CO_2 mixing ratios near those of the atmosphere. The measured air-broadening parameters show several percent deviations (0.9%–2.7%) from values found in the HITRAN 2008 database. Spectra were fit with a variety of models including the Voigt, Galatry, Nelkin-Ghatak, and speed-dependent Nelkin-Ghatak line profiles. Clear evidence of line narrowing was observed, which if unaccounted for can lead to several percent biases. Furthermore, it was observed that only the speed-dependent Nelkin-Ghatak line profile was able to model the spectra to within the instrumental noise level because of the concurrent effects of collisional narrowing and speed dependence of collisional broadening and shifting.

Additional Information

© 2011 American Institute of Physics. Received 1 July 2011; accepted 21 July 2011; published online 12 August 2011. David A. Long was supported by the National Science Foundation and National Defense Science and Engineering Graduate Fellowships. Daniel K. Havey was supported by a National Research Council postdoctoral fellowship at the National Institute of Technology (NIST), Gaithersburg, MD, and Katarzyna Bielska and Daniel Lisak were supported by the Polish MNISW Project No. N N202 1255 35. Part of the research described in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). Additional support was provided by the Orbiting Carbon Observatory (OCO) project, a NASA Earth System Science Pathfinder (ESSP) mission; the NASA Upper Atmospheric Research Program grants NNG06GD88G and NNX09AE21G; the NASA Atmospheric Carbon Observations from Space (ACOS) grant 104127-04.02.02; and the NIST Greenhouse Gas Measurements and Climate Research Program.

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