Multispectrum fitting of line parameters for 12C2H2 in the 3.8-μm spectral region

Abstract Using FT spectra (Bruker IFS 120, unapodized FWHM resolution ≈ 0.001 cm −1 ) of acetylene 12 C 2 H 2 , absolute positions and intensities have been measured for about 250 lines between 2600 and 2800 cm −1 in the ν 2 + ν 5 1 and ( 3 ν 4 + ν 5 ) + 0 cold bands, and in the ν 1 - ν 5 1 , ν 3 - ν 4 1 , and ν 2 + ( ν 4 + ν 5 ) 0 + - ν 4 1 hot bands. These measurements improve the accuracy of wavenumbers previously available and lead to individual line intensities for the first time in this spectral region. A multispectrum fitting procedure has been used to retrieve line parameters from five experimental spectra recorded at different pressures. The frequencies of the ν 3 band of 12 C 16 O 2 allowed to perform an absolute wavenumber calibration. The accuracy of the amount of 12 C 2 H 2 in the sample has been checked using the 3 ν 5 1 cold band around 2100 cm −1 , and has been estimated to be around ±2%. The average absolute accuracy of the line parameters obtained in this work has then been estimated to be ±0.0002 cm −1 for line positions, and ±5% for line intensities. For each studied band, the vibrational transition dipole moment squared value has been determined, as also empirical Herman–Wallis coefficients. A complete line list containing positions and intensities for the five strongest bands around 3.8 μm has been set up for atmospheric applications.