Observations of Dicke narrowing and speed dependence in air-broadened CO₂ lineshapes near 2.06 μm.
Frequency-stabilized cavity ring-down spectroscopy was used to study CO2 lineshapes in the (20013) ← (00001) band centered near 2.06 μm. Two rovibrational transitions were chosen for this study to measure non-Voigt collisional effects for air-broadened lines over the pressure range of 7 kPa-28 kPa. Lineshape analysis for both lines revealed evidence of simultaneous Dicke (collisional) narrowing and speed-dependent effects that would introduce biases exceeding 2% in the retrieved air-broadening parameters if not incorporated in the modeling of CO2 lineshapes. Additionally, correlations between velocity- and phase/state changing collisions greatly reduced the observed Dicke narrowing effect. As a result, it was concluded that the most appropriate line profile for modeling CO2 lineshapes near 2.06 μm was the correlated speed-dependent Nelkin-Ghatak profile, which includes all of the physical effects mentioned above and leads to a consistent set of line shape parameters that are linear with gas pressure.
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
Thinh Q
TQ
Bui
Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.
David A
DA
Long
Institute of Physics, Faculty of Physics, Astronomy, and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland.
Agata
A
Cygan
Material Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, USA.
Vincent T
VT
Sironneau
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
Daniel W
DW
Hogan
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
Priyanka M
PM
Rupasinghe
Institute of Physics, Faculty of Physics, Astronomy, and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland.
Roman
R
Ciuryło
Institute of Physics, Faculty of Physics, Astronomy, and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland.
Daniel
D
Lisak
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
Mitchio
M
Okumura