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International audience; The high-resolution absorption spectrum of acetylene has been recorded at room temperature by high sensitivity cavity ring down spectroscopy (CRDS) in the 6627-7065 cm-1 region. The studied spectral range corresponds to a spectral interval of very weak absorption (an acetylene transparency window). The positions and intensities of more than 7000 lines are determined in the considered interval where previous intensity information was mostly missing. On the basis of previous studies and on effective Hamiltonian predictions, 3062 12C2H2, 462 12C13CH2 and 104 12C2HD absorption lines belonging to a total of 123 vibrational bands are assigned. For comparison, the HITRAN2016 database provides line parameters of only ten 12C2H2 bands in the same region. Spectroscopic parameters of 113 upper vibrational levels were derived from standard band-by-band fits of the line positions (typical rms values of the (obs.-calc.) deviations are better than 0.003 cm-1). Many bands are found to be affected by perturbations. The vibrational transition dipole moment squared and Herman-Wallis coefficients of 47 bands were derived from a fit of the measured intensity values. In order to generate a recommended line list in the region, the derived spectroscopic parameters and Herman-Wallis coefficients were used to compute the line parameters for these 47 bands while experimental position and intensity values were kept for the other bands. Overall, the obtained recommended list including a total of 5260 transitions will help to fill a spectral gap around 1.47 µm where very scarce spectroscopic information is provided in the current spectroscopic databases. When compared to the HITRAN list in the region, some important deviations concerning both line positions and line intensities are evidenced as a result of inaccurate high J extrapolations.

The ESA project „SEOM-Improved Atmospheric Spectroscopy Databases (IAS)“ will improve the spectroscopic database for retrieval of the data products CO, CH4, O3 and SO2 column amounts measured by the TROPOMI instrument (TROPOspheric Monitoring Instrument) aboard the Sentinel-5 Precursor. The project was launched in February 2014 with 3 years duration extended to 4 years recently. The spectroscopy of CO, CH4 and O3 in the 2.3 ?m region is covered first while UV measurements of SO2 and UV/FIR/IR measurements of ozone will be carried out later. Measurements were mainly taken with a high resolution Fourier Transform spectrometer combined with a coolable multi reflection cell. Cavity ring down measurements served for validation. The analysis has been completed. A clear improvement can be seen when using the new data for CH4, H2O and CO retrieval from ground-based high resolution solar occultation measurements obtained with instrumentation in the TCCON and NDACC network.

Due to the increasing performances of Airborne- and ground-based spectrometers, a more and more accurate characterization of the water vapor absorption is required. This is especially true in the transparency windows, corresponding to low absorption spectral regions widely used for probing the Earth’s atmosphere. State-of-the-art experimental developments are required to fulfill the needs in terms of accuracy of the spectroscopic data. For that purpose, we are using high-sensitivity Continuous Wave Cavity Ring Down Spectroscopy (CW-CRDS) allowing reproducing in laboratory conditions comparable to the atmospheric ones in terms of absorption path length (tens of kilometers), temperature and pressure. From extensive analysis of our CRDS spectra, we have constructed an empirical line list for ”natural” water vapor at 296 K in the 5850 7920 cm−1 region including 38 318 transitions of four major water isotopologues (H2 16O, H218O, H217O and HD16O) with an intensity cut-off of 1·10−29 cm/molecule. The list is made mostly complete over the whole spectral region by including a large number of unobserved weak lines with positions calculated using experimentally determined energy levels and intensities obtained from variational calculations. In addition, we provide HD18O and HD 17O lists in the same region for transitions with intensities larger than 1·10−29 cm/molecule. The HD18O and HD17O lists (1 972 lines in total) were obtained using empirical energy levels available in the literature and variational intensities. The global list (40 290 transitions) including the contribution of the six major isotopologues has been adopted for the new edition of the GEISA database in the region. The advantages and drawbacks of our list will be discussed in comparison with the list provided for the same region in the 2012 edition of the HITRAN database. Separate experiments were dedicated to the measurement of the water vapor self-continuum crosssections in the 1.6 µm window by CW-CRDS at different temperatures (from room temperature to 340 K). Due to the weakness of the broadband absorption signal to be measured, very few measurements of the water vapor continuum are available in the NIR windows especially for temperature conditions relevant for our atmosphere. This is in particular the case for the 1.6 µm window where the very few available measurements show a large disagreement. The absorption cross-sections, Cs(ν, T), were retrieved for different selected wave numbers from a fit of the absorption coefficients measured in real time during pressure ramps, after subtraction of the contributions of the local water monomer lines and of water adsorbed on the CRDS mirrors. The values measured between 5875 and 6665 cm−1 range between 1.5·10−25 and 2·10−24 cm2 molec−1 atm−1 with a minimum around 6300 cm−1. Overall, our measurements are found in strong disagreement with recent FTS measurements and in a good agreement with the values predicted by the MT CKD2.5 model, except for the temperature dependence in the center of the window which is found significantly smaller than predicted.

High-energy states of ozone16O3and18O3isotopologues were predicted from a newab initiopotential energy surface1and derived from experimental spectra analysis up to 7920 cm−1. A brief outline is given for highly accurateab initio2calculations and for new analytical PES modeling. The new analytical PES of ozone takes into account such structural properties of ozone as non-linear minimum energy path and non-additivity of the fragmentation energy. The ”reef structure” (activation barrier) problem is investigated as well as its influence on the shifting of harmonic frequencies and vibrational energy levels of ozone. Correction ofab initiodata was made by accounting for the couplings of many excited electronic states3. It is shown that this correction leads to a smoother PES with the ”reef structure” almost vanishing. The PES ”without reef structure” appears to be more precise in terms of spectroscopy: vibration energies are in good agreement with available experimental data4,5,6up to 94% of the dissociation energy with an average error of vibrational prediction near 1 cm−1, which is much better than all available calculations that involve the activation barrier on the transition state.

collection of articles based on oral presentation at the EUMETRISPEC workshop held at Wolfenbüttel castle and PTB Praunschweig, Nov. 15-16, 2012, PTB-Bericht Chemische Physik CP-8. ISSN 1614-953X. ISBN 978-3-95606-034-2., This PTB report comprises all oral presentations and posters presented at the Nov. 2012 workshop on "Spectral reference line data for atmospheric monitoring" held at Wolfenbüttel castle and PTB Braunschweig. The workshop was organized by the EUMETRISPEC project which is part of the European Metrology Research Programme (EMRP). The main aim was to present and discuss the stakeholders' views and needs. The stakeholders are from metrological organisations as well as from ground- and satellite-based monitoring networks and from quantum chemical modelling groups - in total 49 scientists representing 31 institutions from 12 nations. During the workshop, nine invited 45min-talks were given, covering spectroscopic and metrological key topics, accompanied by six additional presentations on EUMETRISPEC and the EMRP. The PTB report includes the authorized powerpoint presentations, as well as all 21 posters from 91 authors presented during the workshop.

International audience; Ozone is a key species in planetary atmospheres. Its important role for the existence of life on Earth and its use as a dynamical and photo-chemical marker for the atmospheres of telluric planets (Mars, Venus) and supposedly also of Earth-like exo-planets make it a preferred object of spectroscopic studies, frequently in the strong bands at 10μm. Existing spectroscopic databases show inconsistencies of some %, however. Motivated by the investigation of the feasibility of a stratospheric wind interferometer (SWIFT) based on ozone absorption at 1133.43351cm-1, which was funded by the Canadian Space Agency, we have undertaken a spectroscopic study of ozone in the 10μm range and at the UV reference wavelength of 253.65nm. Our results suggest a correction of both, the currently recommended reference value in the UV and the infrared intensities. Other uncertainties in the spectroscopic databases are also discussed.