r0pt Figure Dijon spectroscopic databases include calculated line lists, in positions and intensities, that are obtained from experimental spectroscopic analyses. They contain 6 molecules: CH₄, C₂H₄, CF₄, SF₆, GeH₄ and RuO₄ and are all compatibles with the XSAMS (XML Schema for Atoms, Molecules, and Solids) format adopted with the Virtual Atomic and Molecular Data Centre (VAMDC) Project. VAMDC, the worldwide consortium which federates atomic and molecular databases through an e-science infrastructure, aims to provide a unique access point for scientists seeking the best atomic and molecular data for their studies. So far, development of new tools allows to easily download and compare data issued from different databases in a single XML document or into the HITRAN2004 format. Making the comparison that easy will help data users in the choice of data that best match their needs. It will also help data producers by checking the consistency of their data.

Sulfur hexafluoride (SF₆) is a very strong greenhouse gas of anthropogenic origin. Its relatively high molecular mass leads to a very dense molecular spectrum which is quite difficult to analyze. Our groups performed recently strong experimental and theoretical efforts in order to assign and model many cold and hot bands of SF₆, allowing to strongly improve the modeling of its atmospheric absorptionM. Faye et al. , J. Quant. Spectrosc. Radiat Transfer 190, 38,47 (2017) ; M. Faye et al. , J. Mol. Spectrosc. in press (2018). We present here a synthesis of the latest available data and global analyses performed thanks to the formalism and programs developed in Dijon. In particular, new progress has been realized towards the modeling of hot bands in the strongly absorbing ν₃ region around 948 cm⁻¹. The results have been used tu fully update the SHeCaSDa database (http://vamdc.icb.cnrs.fr/PHP/shecasda.php) which is also accessible from the VAMDC portal (http://portal.vamdc.org) and will be included in future HITRAN and GEISA updates.

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Footnotes:

M. Faye et al. , J. Quant. Spectrosc. Radiat Transfer 190, 38,47 (2017) ; M. Faye et al. , J. Mol. Spectrosc. in press (2018)..

Modelling correctly the SF₆ atmospheric absorption requires the knowledge of the spectroscopic parameters of all states involved in the many hot bands in the 10 μm atmospheric window used for remote sensing. Since a direct analysis of the hot bands near the ν₃ absorption of SF₆ in this atmospheric window is not possible, due to their overlapping, we use another strategy, gathering information in the far and mid infrared regions on initial and final states to compute the relevant total absorption. In this talk, we present new results of an analysis of spectra recorded at the AILES beam line at the SOLEIL Synchrotron facility. For these measurements, we used an IFS125HR interferometer in the 100 to 3200 cm⁻¹range, coupled to a cryogenic multiple pass cell. The optical path length was varied from 45 to 141 m with 223 and 153 K temperatures. New information has been obtained on the ν₃ + ν₅ band which, combined with improved parameters for ν₅, is used to model the important ν₃+ν₅ - ν₅ hot band contribution [1]. Also, data have been obtained on the ν₃ band of the ³⁶SF₆ isotopic species present in very low abundance (0.0002) [2]. These new parameters will be included in the XTDS model [3] and VAMDC/SheCaSDa database [4], thus improving the previous SF₆ parameters. [1] M. Faye, L. Manceron, P. Roy, V. Boudon, M. Loete, “First analysis of the ν₃+ν₅ combination band of SF₆ observed at Doppler-limited resolution and effective model for the ν₃+ν₅-ν₅ hot band” J. Mol. Spectrosc., in press. [2] M. Faye, L. Manceron, P. Roy, V. Boudon, M. Loete, “First high resolution analysis of the ν₃ band of the ³⁶SF₆ isotopologue”, J. Mol. Spectrosc., in press. [3] C. Wenger, V. Boudon, M. Rotger, M. Sanzharov, and J.-P. Champion,”XTDS and SPVIEW: Graphical tools for Analysis and Simlation of High Resolution Molecular Spectra”, J. Mol. Spectrosc. 251, 102 (2008). [4] http://vamdc.icb.cnrs.fr/PHP/shecasda.php

The Montreal Protocol has banned the production of major ozone depleting substances such as chlorofluorocarbons (CFCs) to protect the Earth’s ozone layer. These chlorinated compounds eventually form a large reservoir of HCl in the upper atmosphere. Therefore, the success of the Montreal Protocol can be determined by measuring the stratospheric HCl abundance. The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) measures infrared solar occultation spectra of the Earth’s atmosphere from which altitude profiles of HCl volume mixing ratios (VMRs) are determined. The stratospheric HCl VMR time series has a linear trend of -4.9±0.4 % per decade for 2004-2017, highlighting the continuing success of the Montreal Protocol. The emission of hydrofluorocarbons (HFCs) has increased in order to replace the CFCs since they are not restricted by the Montreal Protocol. As a result, the atmospheric abundance of HFCs are rapidly increasing. Even though these HFCs do not contribute to the depletion of the ozone layer, they are powerful greenhouse gases with large global warming potentials. In 2016, the Kigali Amendment to the Montreal Protocol was introduced in order to phaseout long-lived HFCs. The VMRs of the two most abundant HFCs in the atmosphere, HFC−134a and CHF₃, are also measured by the ACE-FTS. These measurements will be useful for monitoring the Kigali Amendment to the Montreal Protocol. The ACE observations and trends for atmospheric HCl, HFC−134a and CHF₃ will be presented.

Fluorine- and chlorine-containing molecules in the atmosphere are very strong greenhouse gases, meaning that even small amounts of these gases contribute significantly to the radiative forcing of climate. In addition, a number of these molecules, such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), are harmful to the Earth's ozone layer and for this reason their use is regulated by the 1987 Montreal Protocol. The recent Kigali Amendment has added hydrofluorocarbons (HFCs) to the list of controlled substances, coming into effect on 1 January 2019. HFCs, which do not deplete stratospheric ozone, were introduced as refrigerant replacements for CFCs and HCFCs. They are potent greenhouse gases, with global-warming potentials many times greater than carbon dioxide, and are increasing in the atmosphere at a very fast rate. A number of satellite instruments, in particular the ACE-FTS (Atmospheric Chemistry Experiment – Fourier Transform Spectrometer), can monitor many of these species by detecting infrared radiation that has passed through the Earth's atmosphere. However, the quantification of their atmospheric abundances crucially requires accurate quantitative infrared spectroscopy. This talk will focus on new and improved laboratory spectroscopic measurements for a number of important halogenated species.

The semi empirical MT_CKD model of the absorption continuum of water vapor is widely used in atmospheric radiative transfer codes of the atmosphere of Earth and, recently, of exoplanets, but lacks of experimental validation in the atmospheric windows. We report on accurate water vapor absorption continuum measurements by Cavity Ring Down Spectroscopy (CRDS) and Optical-Feedback-Cavity Enhanced Laser Spectroscopy (OF-CEAS) at selected spectral points of the transparency windows centered around 4.0, 2.1, 1.6 and 1.25 μm. Temperature dependence of the absorption continuum is also measured in the 23-50 ^°C range for a few spectral points. The self-continuum water vapor absorption is derived either from the baseline variation of water vapor spectra recorded for a series of pressure values over a small spectral interval or from baseline monitoring at fixed laser frequency during pressure ramps. After subtraction of the local water monomer lines contribution, self-continuum cross-sections, C_S, are accurately determined from the pressure squared dependence of the continuum absorption measured up to about 15 Torr. The derived water vapor self-continuum provides a unique set of water vapor self-continuum cross-sections for a test of the MT_CKD model in four transparency windows.

We present a new ab initio dipole moment surface (DMS) for the water molecule valid for transitions which stretch into the near ultraviolet. Intensities computed using this surface agree very well with precise laboratory measurements designed to aid atmospheric observations. This work is based on a data set encompassing 17 628 multi-reference configuration interaction configurations that were calculated with the aug-cc-pCV6Z basis set with the Douglass-Kroll-Hess Hamiltonian to second order and required approximately 116 years of CPU running time to complete. Compared to recent experimental measurements in the far infrared regionM. Birk et al., J. Quant. Spectrosc. Rad. Transf, 203, 88-102 (2017) this new DMS significantly improves agreement with theory for transitions in the previously problematic bands (121), (300) and (102). For highly energetic overtones located in both the visible and ultraviolet regimes, we successfully predict the intensity of all measured bands to within 10% of the latest atmospheric observations J. Lampel et al., Atmos. Chem. Phys, 17, 1271-1295, (2017) These include bands at 487 nm (303), 471 nm (511), and 363 nm (900), for which previous models underestimated the intensity by up to 139%. Absorption features are also predicted in the 290 nm to 355 nm window and the theoretical shape demonstrates reasonably good behaviour with previously measured cross sections. The 10 ν₁ band is identified as the strongest absorber in this region and the maximum intensity is approximately 6.3×10⁻²⁷ cm per molecule, which should be observable in atmospheric spectra.

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Footnotes:

M. Birk et al., J. Quant. Spectrosc. Rad. Transf, 203, 88-102 (2017), J. Lampel et al., Atmos. Chem. Phys, 17, 1271-1295, (2017).

Isoprene (C₅H₈) is the most abundant biogenic volatile organic compound (BVOC) emitted by plants into Earth’s atmosphere and plays a key role in the chemistry of the troposphere. Isoprene (and other BVOCs) play a role in the formation of secondary organic aerosols and production of tropospheric ozone, a pollutant that is a major part of photochemical smog. One attractive means of measuring isoprene levels in the atmosphere is the use of infrared spectroscopy to monitor strong absorption bands that lie in the “atmospheric window” between 8-14 μm. We have measured the high-resolution infrared spectrum of isoprene in the region of the strong ν₂₆ vibrational band near 10 μm using a quantum cascade laser-based spectrometer. This work will support future efforts to use the ν₂₆ band for sensing applications. We will discuss the assignment of several weaker bands we have observed near the main ν₂₆ band and a rotational analysis based on the strong Q-branches. In addition, we have also observed the high-resolution spectrum of methyl vinyl ketone (C₄H₆O), an oxidation product of isoprene, in this same frequency region, and will present a preliminary analysis of our spectrum.