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

Using FT spectra (Bruker IFS 120, unapodized FWHM resolution ≈ 0.001 cm−1) of acetylene 12C2H2, absolute positions and intensities have been measured for about 250 lines between 2600 and 2800 cm−1 in the ν2+ν51 and (3ν4+ν5)+0 cold bands, and in the ν1-ν51,ν3-ν41, and ν2+(ν4+ν5)0+-ν41 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 ν3 band of 12C16O2 allowed to perform an absolute wavenumber calibration. The accuracy of the amount of 12C2H2 in the sample has been checked using the 3ν51 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.