 ( ) 0+   ( ) 0–  4 1 Results at 2.5 microns 2 +( ) 1 II ( ) 2  4 1 Recent knowledge of spectroscopic parameters for Acetylene in the IR D. Jacquemart, a N. Lacome, a V. Dana, b J.-Y. Mandin b, O.M. Lyulin c, V.I. Perevalov c, L. Régalia-Jarlot d, X. Thomas d, P. Von Der Heyden d a Laboratoire de Dynamique, Interactions et Réactivité, Université Pierre-et-Marie Curie, CNRS, UMR 7075, Case courrier 49, 4, place Jussieu, Paris Cedex 05, France b Laboratoire de Physique Moléculaire pour l’Atmosphère et l’Astrophysique, Université Pierre-et-Marie-Curie, CNRS, UMR 7092, Case courrier 76,4, place Jussieu,75252 Paris Cedex 05, France c Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences, 1, Akademicheskii av., Tomsk, Russia d Groupe de Spectrométrie Moléculaire et Atmosphérique, Université de Reims-Champagne-Ardenne, CNRS, BP 1039, Reims Cedex, France. References: [1] D. Jacquemart, N. Lacome, J.-Y. Mandin, V. Dana, O.M. Lyulin, V.I. Perevalov. Multispectrum fitting of line parameters for 12 C 2 H 2 in the 3.8-μm spectral region. (submitted to JQSRT) [2] O.M. Lyulin, V.I. Perevalov, J.-Y. Mandin, V. Dana, F. Gueye, X. Thomas, P. Von Der Heyden, D. Décatoire, L. Régalia-Jarlot, D. Jacquemart, N. Lacome. Line intensities of acetylene: Measurements in the 2.5-µm spectral region and global modeling in the  P = 4 and 6 series. (submitted to JQSRT) [3] O.M. Lyulin A, V.I. Perevalov, F. Gueye, J.-Y. Mandin, V. Dana, X. Thomas, P. Von Der Heyden, L. Régalia-Jarlot, A. Barbe. Line intensities of acetylene. Measurements in the 2.2-µm spectral region and global modeling in the  P = 7 series (under editing) [4] O.M. Lyulin, V.I. Perevalov, S.A. Tashkun, and J.-L. Teffo. Global fitting of the vibrational-rotational line positions of acetylene molecule in the far and middle infrared regions. In: Proceedings of the XIVth Symposium on High-Resolution Molecular Spectroscopy, Krosnoyarsk, Russia. SPIE 5311, (2004). [5] V.I. Perevalov, O.M. Lyulin, D. Jacquemart, C. Claveau, J.-L. Teffo, V. Dana, J.-Y. Mandin, and A. Valentin. Global fitting of line intensities of acetylene molecule in the infrared using the effective operator approach. J Mol Spectrosc 218, (2003). [6] D. Jacquemart, J.-Y. Mandin, V. Dana, N. Picqué, and G. Guelachvili. A multispectrum fitting procedure to deduce molecular line parameters. Application to the 3  0 band of 12 C 16 O. Eur Phys J D 14, (2001). PRESENTATION The acetylene molecule is important for atmospheric, planetary, and astrophysics applications. In order to improve the knowledge of C 2 H 2 spectroscopic parameters, systematic measurements of line parameters have been performed. Three recent works in three different spectral regions are presented: in the 3.8-μm region, where 2 cold and 3 hot bands have been studied [1]; in the 2.5-μm region, where 4 cold and 5 hot bands have been studied [2]; in the 2.2-μm region, where 4 cold and 4 hot bands have been studied [3]. Line positions and intensities have been analysed. In these three spectral regions, transition dipole moments squared values have been derived from the line intensity measurements, and have been modelled using Herman- Wallis factors. No analysis of absolute individual line intensities in these three regions has been done before these present works. Line lists have been generated and will be proposed to atmospheric and planetary spectroscopic databases. The analysis of these spectral region has also allowed to improve the global theoretical treatment [4-5] of Perevalov et al. adapted to the Hamiltonian and transition dipole moment of acetylene 12 C 2 H 2 ( interacting vibrational states belonging to different polyads are taken into account through cold and hot bands ). According to Perevalov’s notation, the studied spectral region concerns the series of vibrational transitions  P = 4, 6 and 7 with P the pseudo-quantum number: P = 5v 1 + 3v 2 + 5v 3 + v 4 + v 5. MEASUREMENT PROCEDURE To retrieve absolute line positions and intensities from the spectra, a multispectrum fitting procedure [6] has been used. Because of the wide variety of the line strength values, the best experimental conditions for an accurate analysis are obtained only for two or three spectra. Due to the flexibility of the multispectrum procedure, we were able to adjust simultaneously all experimental spectra. Let us recall that the position, intensity, and broadening coefficient of a same line in the five spectra keep the same values during the fit. In a first step, a wavenumber calibration has been done separately for the three spectral regions. Transitions of the ν 3 band of 12 C 16 O 2 has been used for the 3.8-μm spectral region; H 2 O transitions and C 2 H 2 transitions respectively for the 2.5- and 2.2-μm spectral regions. ε = (σ HITRAN σ this work )/ σ HITRAN2004 has been calculated for isolated transitions in each spectrum. Combining the absolute accuracy from HITRAN2004 and the statistic deviation of our wavenumber calibration, we estimated that the absolute accuracy of the measured positions is around cm -1. As an example of the capability of our multispectrum fitting procedure, this figure shows a simultaneous fit of the Q- branch of the ν 2 + ν 5 1 of 12 C 2 H 2 in 4 spectra recorded at different pressures. The calculated spectra reproduce very well each experimental spectrum. For each of them, the residuals (obs-calc) of the fit are quite good despite the two channels (due to windows) present in the experimental spectra. The residuals of the fit do not exceed 2%. ANALYSIS OF THE SQUARED DIPOLE TRANSITION MOMENT The determination of the squared dipole transition moment R 2 is obtained from the line intensity using the following equation: The quantities F(m) (calculated using the Herman Wallis coefficients), and |R 0 | (vibrational dipole transition moment) are fitting for each P-and R-branch and Q-branch the following equations: mm cm … … 9600 Polyads defined by P the pseudo-quantum number: P = 5v 1 + 3v 2 + 5v 3 + v 4 + v 5 ΔPΔP … 15 v 1 = 3373 cm -1 ; v 2 = 1974 cm -1 ; v 3 = 3294 cm -1 ; v 4 = 613 cm -1 ; v 5 = 730 cm -1 CONCLUSION Several collaborations between LADIR, LPMAA, GSMA, and LTS has led to the better knowledge of the acetylene IR spectroscopic parameters in the 2.2, 2.5, and 3.8-μm spectral regions. The experimental results in the 2.5 and 3.8-μm regions have allowed the generation of line lists with calculated positions (obtained from polynomial fits of measurements), and calculated intensities (using the transition dipole moment and the Herman-Wallis coefficients of each band). This has not been done for the 2.2-μm region where strong interactions between levels do not allow accurate fit using Herman-Wallis coefficients. All the measurements have then been used to treat the ΔP = 4, 6 and 7 series. The first results are encouraging, but at that time the precision of the line positions and intensities obtained using treatment of the Hamiltonian and the transition dipole moment, is not enough accurate compared to the one from experimental measurements. The global model of acetylene done by LTS (Perevalov et al.) still need some improvement, and measurements to achieve the experimental accuracy that is better than cm -1 for positions, and 5% for line intensities. Note that, the predictability of this model was successfully tested on two hot bands of the 2.5-μm region [2]. Results at 2.2 microns 1 +( ) ( ) ( ) 1  ( ) 1   ( ) 1  4 1 Global treatment of ΔP = 4 and 6 series Results at 3.8 microns Transmission 1,4 cm -1