Fig. 4

Measured spectrum of C₂H₂. a) The spectrum obtained from a continuous 500 s recording, phase corrected every 100 s and averaged. Absorption lines originate from the 8-cm-long gas cell filled with 29 mbar C₂H₂ of natural abundance. b) Portions of the absorption lines in (a), which show fine modulation structure clearly in the bottom panel. c) Comparison between the extracted absorption lines (blue line) and the theoretical absorbance spectra (red line) of C₂H₂ computed using the HITRAN line parameters. d) Portions of absorption lines in (c), showed good agreement between the measured absorption lines (blue scatter) and the curve profiles from HITRAN