Global analysis of several bands of the CF4 molecule

Carbon tetrafluoride is a powerful greenhouse gas, mainly of anthropogenic origin. Its absorption spectrum is, however, still badly modeled, especially for hot bands in the strongly absorbing $\nu_3$ region. To overcome this problem, we have undertaken a systematic study of all the lower rovibrational transitions of this molecule. In particular, new far-infrared spectra recorded at the SOLEIL Synchrotron facility give access to bands implying the ``forbidden'' modes $\nu_1$ and $\nu_2$ which have only been investigated previously thanks to stimulated Raman spectroscopy\footnote{V. Boudon, D. Bermejo, R. Z. Mart\'{\i}nez, J. Raman Spectrosc. {\bf 44}, 731?738 (2013).}, that is with a lower accuracy and much less data. Combined with the previous analyses performed in our group\footnote{V. Boudon, J. Mitchell, A. Domanskaya, C. Maul, RGeorges, A. Benidar, W. G. Harter, Mol. Phys. {\bf 109}, 17--18 (2011).}, we thus report here a new global fit of line positions of CF$_4$ by considering several transitions altogether: $\nu_2$, $2\nu_2-\nu_2$, $\nu_4$, $2\nu_4$, $\nu_3$ and $\nu_3-2\nu_2$. This gives a consistent set of molecular parameters that will be of great help for the analysis of hot bands like $\nu_3+\nu_2-\nu_2$. A second separate global fit including the $\nu_1$, $\nu_1-\nu_4$ and $2\nu_1-\nu_1$ bands will also be presented

High-resolution stimulated raman spectroscopy and analysis of V2 and V3 bands of of 13C2H4 using the D2H top data system

High resolution stimulated Raman spectra of $^{13}$C$_2$H$_4$ in the regions of the $\nu_2$ and $\nu_3$ Raman active modes have been recorded at at two temperatures (145 and 296 K) based on the quasi continuous-wave (cw) stimulated Raman spectrometer at Instituto de Estructura de la Materia (CSIC) in Madrid. A tensorial formalism adapted to $X_{2}Y_{4}$ planar asymmetric tops with $D_{2h}$ symmetry has been developed in Dijon\footnote{Raballand W, Rotger M, Boudon V, Lo{\"e}te M. J Mol Spectrosc 2003217:239--48.} and a program suite called $D_{2h}TDS$ (now part of the XTDS/SPVIEW spectroscopic software\footnote{Wenger Ch, Boudon V, Rotger M, Champion JP, Sanzharov M. J Mol Spectrosc 2008251:102--13.} was proposed to calculate their high-resolution spectra. The effective Hamiltonian operator, involving a polyad structure, and transition moment (dipole moment and polarizability) operators can be systematically expanded to carry out global analyses of many rovibrational bands. A total of 103 and 51 lines corresponding to $\nu_2$ and $\nu_3$ Raman active modes have been assigned and fitted in frequency with a global root mean square deviation of $0.54 \times 10^{-3}$ cm$^{-1}$ and $0.36 \times 10^{-3}$ cm$^{-1}$, respectively. The figures below shows the stimulated Raman spectrum of the $\nu_2$ and $\nu_3$ bands of $^{13}$C$_2$H$_4$, compared to the simulation at 296 K

Global analysis of the high temperature infrared emission spectrum of 12CH4 in the dyad (ν2/ν4) region

We report new assignments of vibration-rotation line positions of methane ($^{12}$CH$_4$) in the so-called Dyad ($\nu_2$/$\nu_4$) region (1000 -- 1500 cm$^{-1}$), and the resulting update of the vibration-rotation effective model of methane, previously reported by Nikitin \textit{et al.} [A.V. Nikitin \textit{et al.} PCCP, \textbf{15}, (2013), 10071], up to and including the Tetradecad. High resolution (0.01 cm$^{-1}$) emission spectra of methane have been recorded up to about 1400 K using the high-enthalpy source developed at IPR associated with the Fourier transform spectrometer of the SOLEIL synchrotron facility (AILES beamline). Analysis of these spectra allowed extending rotational assignments in the well-known cold band (Dyad$-$GS) and related hot bands in the Pentad$-$Dyad system (3000 cm$^{-1}$) up to $J_{max}=30$ and 29, respectively. In addition, 8512 new transitions belonging to the Octad$-$Pentad (up to $J=28$) and Tetradecad$-$Octad (up to $J=21$) hot band systems were successfully identified. As a result, the MeCaSDa database of methane was significantly improved. The line positions assigned in this work, together with the information available in the literature, were fitted using 1096 effective parameters with a dimensionless standard deviation $\sigma = 2.09$. The root mean square deviations $d_{RMS}$ are 3.60 $\times 10^{-3}$ cm$^{-1}$ for Dyad$-$GS cold band, 4.47 $\times 10^{-3}$ cm$^{-1}$ for the Pentad$-$Dyad, 5.43 $\times 10^{-3}$ cm$^{-1}$ for the Octad$-$Pentad and 4.70 $\times 10^{-3}$ cm$^{-1}$ for the Tetradecad$-$Octad hot bands. The resulting new line list will contribute to improve opacity and radiative transfer models for hot atmospheres, such as those of hot-Jupiter type exoplanets

HIGH-RESOLUTION INFRARED SPECTRA AND ANALYSES OF SiF4

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.2]{Fig_nu3.eps} \end{wrapfigure} Volcanoes reject large amounts of sulfur-containing gases in the atmosphere; these represent 10 to 15~\% of the anthropogenic sulfur emissions. Thermodynamic considerations show that silicon tetrafluoride (SiF$_4$) should be a normal trace component of volcanic gases. Some studies report that the possible importance of SiF$_4$ had been neglected because of the problems of reporting HF and SiF$_4$ separately in conventional analyses. However, a better knowledge of spectroscopic parameters is needed for this molecule in order to derive accurate concentrations. This is why we undertook an extensive high-resolution study of its infrared absorption bands, including the fundamentals and several overtone and combinations. We present here a detailed analysis and modeling of the strongly absorbing $\nu_3$ fundamental, for the there isotopplogues in natural abundance: ${}^{28}$SiF$_4$ (92.23~\%), ${}^{29}$SiF$_4$ (4.67~\%) and ${}^{30}$SiF$_4$ (3.10~\%). Progresses in the analysis of the other bands will be outlined

EXO-PLANETARY HIGH-TEMPERATURE HYDROCARBONS BY EMISSION AND ABSORPTION SPECTROSCOPY (e-PYTHEAS PROJECT)

e-PYTHEAS is a multidisciplinary project which combines theoretical and experimental work with exoplanet modelling applications. It sits on the frontier between molecular physics, theoretical chemistry and astrophysics. It aims at enhancing our understanding of the radiative properties of hot gaseous media to allow for improved analysis and interpretation of the large mass of data available on the thousands of exoplanets and exoplanetary systems known to date. Our approach is to use theoretical research validated by laboratory experiments and to then inject it into models of the atmospheres of the giant gaseous planets in the solar system and other planetary systems. This will help to analyse data and address essential questions on the formation and evolution of planetary systems, such as retrieved by ESA's M4 space mission ARIEL. Our consortium of 5 French laboratories and associated partners proposes to improve the existing high-temperature spectroscopy data for several molecular species detected in exoplanets. The provision of infrared (IR) laboratory data of methane, acetylene, ethylene and ethane, between 500 and 2500 K will help to refine thermal profiles and provide information on the gaseous composition, the hazes and their temporal variability. See the project's website: http://e-pytheas.cnrs.f

LINE POSITIONS OF CENTRIFUGAL DISTORSION INDUCED ROTATIONAL TRANSITIONS OF METHANE MEASURED UP TO 2.6 THZ AT SUB-MHZ ACCURACY WITH A CW-THZ PHOTOMIXING SPECTROMETER

Several Doppler limited rotational transitions of methane induced by centrifugal distortion have been measured with an unprecedented frequency accuracy using the THz photomixing synthesizer based on a frequency comb. Compared to previous synchrotron based FT-Far-IR measurements of Boudon {em et al./}footnote{V. Boudon, O. Pirali, P. Roy, J.-B. Brubach, L. Manceron, J. Vander Auwera, J. Quant. Spectrosc. Radiat. Transfer, {bf 111}, 1117--1129 (2010).}, the accuracy of the line frequency measurements is improved by one order of magnitude, this yields a corresponding increase of two orders of magnitude to the weighting of these transitions in the global fit. The rotational transitions in the $nu_4leftarrownu_4$ hot band are measured for the first time by the broad spectral coverage of the photomixing CW-THz spectrometer providing access up to $R(5)$ transitions at 2.6 THz. The new global fit including the present lines has been used to update the methane line list of the HITRAN database. Some small, but significant variations of the parameter values are observed and are accompanied by a reduction of the $1$-$sigma$ uncertainties on the rotational ($B_0$) and centrifugal distortion ($D_0$) constants._x000d

ON THE IMPORTANCE OF FAR-INFRARED SPECTROSCOPY FOR NON-POLAR SPHERICAL-TOP MOLECULES

Highly-symmetric molecules like spherical-top possess no permanent dipole moment. Thus, at least in first approximation, their pure rotation spectrum is forbidden (or even strictly forbidden in the case of centrosymmetric species). It may thus seem useless to consider their far-infrared or THz spectrum. Nevertheless, this spectral region can provide invaluable information for these molecules. Firstly, in the case of tetrahedral species of type XY$_4$, pure rotation lines in the ground or in excited vibrational states can be induced through centrifugal distortion. Secondly, the strict selection rules for spherical-top molecules make some fundamental levels inaccessible though direct absorption. Here again, far-infrared studies can help to reach them through the study of low-lying difference bands. Thirdly, some larger and/or heavier species possess weak bands at low wavenumbers. In this talk, we will summarize some recent studies performed on the AILES beamline of the SOLEIL Synchrotron facility that illustrate these different cases with CH$_4$, CF$_4$, OsO$_4$, RuO$_4$, C$_{10}$H$_{16}$, C$_6$N$_4$H$_{10}$, C$_8$H$_8$ and SF$_6$

LINE POSITIONS AND INTENSITIES FOR THE ν3 BAND OF 5 ISOTOPOLOGUES OF GERMANE FOR PLANETARY APPLICATIONS

Germane (GeH$_4$) is present in the atmospheres of the giant planets Jupiter and Saturn. The ongoing NASA mission Juno has renewed interest in its spectroscopy. The accurate modeling of which is essential for the retrieval of other tropospheric species. We present here the first complete analysis and modeling of line positions and intensities in the strongly absorbing $\nu_1/\nu_3$ stretching dyad region near 2100~cm$^{-1}$, for all five germane isotopologues in natural abundance\footnote{V. Boudon, T. Grigoryan, F. Philipot, C. Richard, F. Kwabia Tchana, L. Manceron, A. Rizopoulos, J. Vander Auwera and T. Encrenaz, {\em J. Quant. Spectrosc. Radiat. Transfer} {\bf 205}, 174--183 (2018)}. New infrared spectra were recorded, absolute intensities were extracted through a careful procedure and modeled thanks to the formalism and programs developed in Dijon. A database of calculated germane lines, GeCaSDa, is available online through the {\em Virtual Atomic and Molecular Data Centre\/} (VAMDC) portal ({\tt http://portal.vamdc.org}) and at {\tt http://vamdc.icb.cnrs.fr/PHP/gecasda.php}. GeH$_4$ will integrate the HITRAN database as molecule number 50

STRONG THERMAL NONEQUILIBRIUM IN HYPERSONIC CO AND CH4 PROBED BY CRDS

A new experimental set-up coupling a High Enthalpy Source (HES) reaching 2000~K to a cw Cavity Ring-Down Spectrometer has been developed to investigate rotationnally cold hot bands of polyatomic molecules in the $[1.5,1.7]$~$mu$m region. The rotational and vibrational molecular degrees of freedom are strongly decoupled in the hypersonic expansion produced by the HES and probed by Cavity Ring-Down Spectroscopy. Carbon monoxide has been used as a first test molecule to validate the experimental approach. Its expansion in argon led to rotational and vibrational temperatures of $6.7pm 0.8$~K and $2006pm 476$~K, respectively. The Tetradecad polyad of methane ($1.67$~$mu$m) was investigated under similar conditions leading to rotational and vibrational temperatures of $13pm 5$~K and $750pm 100$~K, respectively. The rotationally cold structure of the spectra reveals many hot bands involving highly excited vibrational states of methane

DETAILED ANALYSIS OF THE INFRARED SPECTRUM OF SiF4: AN UPDATE

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.2]{Fig_nu4.eps} \end{wrapfigure} Silicon tetrafluoride (SiF$_4$) should be a normal trace component of volcanic gases. However, a better knowledge of spectroscopic parameters is needed for this molecule in order to derive accurate concentrations. As explained last year, we undertook an extensive high-resolution study of its infrared absorption bands, for the there isotopologues in natural abundance: ${}^{28}$SiF$_4$ (92.23~\%), ${}^{29}$SiF$_4$ (4.67~\%) and ${}^{30}$SiF$_4$ (3.10~\%). We present here an update of this study. It includes a new global fit with consistent parameter sets for the ground and excited states (the Figure on the right presents the $\nu_4$ bending fundamental region). In particular, all existing rotational line data have been included. The $2\nu_4$ band of ${}^{28}$SiF$_4$ could also be analyzed in detail. A first rough estimates of the dipole moment derivative for the $\nu_3$ band has been performed, leading to to an integrated band intensity which is consistent with literature values, around $680$~km$/$mol. The isotopic dependance of band centers and Coriolis parameters has been studied, thanks to the formula presented in talk P4363