V. Zéninari, L. Joly, B. Grouiez, B. Parvitte, A. Barbe

1. Observations of SO2 spectra with a quantum cascade laser spectrometer around 1090 and 1160 cm-1. Comparison with HITRAN database and updated calculations V. Zéninari, L. Joly, B. Grouiez, B. Parvitte, A. Barbe Groupe de Spectrométrie Moléculaire et Atmosphérique, UMR CNRS 6089, UFR Sciences Exactes et Naturelles, Moulin de la Housse, BP 1039, 51687 Reims, Cedex 2, France Due to its application into atmospheric environment and astrophysics, the infrared spectrum of SO2 has been the subject of many studies. Since the first realization of a quantum cascade laser (QCL) in 1994, many applications have been studied: communications, detection and quantification of trace gases, and high-resolution spectroscopy. Some years ago we had reported about spectroscopic studies of the ν1 band of SO2 using a continuous wave QCL [i] where line intensities and self-broadening coefficients had been measured for 9 isolated lines of SO2 between 1088 and 1090 cm-1. New spectra recorded in this region have been compared with previous determinations and theoretical predictions. Line positions, line strengths and self-broadening coefficients have shown some discrepancies with those of the HITRAN database. Several lines found in this study were not present in the HITRAN database. In order to have a complete linelist of transitions of SO2 appearing into the experimentally recorded spectra at 9 µm, we have performed a new calculation of the ν1 band of 32SO2, the ν1 + ν2 – ν2 band of 32SO2 and the ν1 band of 34SO2. This new calculation demonstrates a dramatic improvement of the calculations of synthetic spectra of SO2. These new calculations improve the positions of the ν1 band of 32SO2 with respect to HITRAN database and permit to obtain a complete set of data of the ν1 + ν2 – ν2 band of 32SO2 and the ν1 band of 34SO2 where the positions and strengths are in excellent agreement with experimental data. This agreement obtained around 1090 cm-1 has been confirmed around 1160 cm-1 with experimental data obtained with another quantum cascade laser spectrometer. [i] Spectroscopic study of the n1 band of SO2 using a continuous wave DFB QCL at 9.1 µm, L. Joly, V. Zéninari, B. Parvitte, D. Weidmann, D. Courtois, Y. Bonetti, T. Aellen, M. Beck, J. Faist, D. Hofstetter, Applied Physics B: Lasers and Optics, 77, 6-7, pp. 703-706, (2003) • Calculation of the spectra: • n1 band of 32SO2: Hamiltonian constants are taken from Flaud et al [JMS 1993] and transition moment parameters from Chu et al [JMS 1998]. Note that this calculation is not included in HITRAN 2004 database but is available on request upon the authors. • ν1 + ν2 – ν2 band of 32SO2: Hamiltonian constants are those obtained in Guelachvili et al [JMS 1987] and we have used the transition moment of 32SO2 from Chu et al [JMS 1998]. • ν1 band of 34SO2: Hamiltonian constants are given in Guelachvili et al [JMS 1987] and intensities are calculated using transition moment of n1 band of 32SO2 from Chu et al [JMS 1998] with the partition function Z (34SO2) = 6373 at 296 K. • All transitions have been obtained using GIP program of Tashkun & Tuyterev. A total of 37436 transitions is obtained with a cut-off of 66 for J, 30 for Ka and intensities of 3 10-25 cm-1/(molecule.cm-2). The intensities of the lines in our compilation are, like in HITRAN database, multiplied by their natural abundance, that is to say 0.94568 for 32SO2 and 0.04195 for 34SO2. Example of calculated spectrum with HITRAN 2004 (upper panel, black line) and with the new calculation of all bands of 32SO2 presented in this work (upper panel, grey line). The lower panel presents the experimental points and the new calculation of all bands of 32SO2 under the same experimental conditions (P = 13.3 mbar, T = 289 K, l = 19.76 cm) using varying self-broadening coefficients with Ka. Example of calculated spectrum with HITRAN 2004 (upper panel, black line), with the new calculation of (100)(000) band of 32SO2 presented in this work (upper panel, grey line) and recorded spectrum (lower panel) under the same experimental conditions (P = 13.3 mbar, T = 289 K, l = 19.76 cm). We can note some shifts in positions and the presence of lines of hot band and 34SO2. Example of calculated spectrum with HITRAN 2004 (upper panel, black line), with the calculation of all bands of SO2 presented in this work (upper panel, grey line) and recorded spectrum (lower panel) under the same experimental conditions (P = 13.3 mbar, T = 289 K, l = 19.76 cm). Examples of calculated spectrum with HITRAN 2004 (black line), with the new calculation of all bands of SO2 presented in this work (grey line) and experimental spectrum under the same experimental conditions (P = 1.97 mbar, T = 293 K, l = 20.4 cm). We can note the problems of positions and the presence of numerous lines of hot band and 34SO2. HITRAN Conference 2006