Multispectrum fitting measurements of line parameters for 5-μm cold bands of acetylene

Abstract

Using FT spectra (unapodized FWHM: 0.002 cm −1 ) of acetylene 12 C 2 H 2 , absolute line positions have been measured (average accuracy: ±0.0002 cm −1 ) between 1860 and 2180 cm −1 in the 3 ν 5 1, (2 ν 4+ ν 5) 1I, and (2 ν 4+ ν 5) 1II cold bands, improving the wavenumbers previously published by Plı́va under a resolution of about 0.03 cm −1 . Absolute intensities have been obtained for more than 130 lines, with a mean accuracy of ±5%, the accuracy of the amount of 12 C 2 H 2 in the sample being estimated to be better than 2%. For each band, the vibrational transition dipole moment squared has been determined, as well as empirical Herman–Wallis coefficients. Self-broadening coefficients have been measured at room temperature for more than 120 lines. No striking vibrational dependence has been observed for the self-broadening coefficients, and a polynomial expansion describing the rotational dependence is given. Furthermore, self-shifting coefficients have been measured for 89 lines, together with more than 150 absolute line positions. A multispectrum fitting procedure has been used to retrieve the line parameters from the spectra, and cross comparisons have been performed on a few lines between two different codings of this procedure.