SUBMILLIMETER WAVE SPECTROSCOPY FOR ISM: IMINES WITH INTERNAL ROTATION

The aldimines are important to understand amino acids formation process as they appear in reaction scheme of Strecker-type synthesis. It seems reasonable to propose syntheses in the solid phase but the formation process is not clearly established. The number of imines and amines detected in the interstellar medium is limited, mainly due to lack of spectroscopic data. We present here the studies of ethanimine (CH$_{3}$CHNH) and methylimino-acetonitrile (CH$_{3}$N=CHCN). Both of them have has two isomers E and Z with E one being the most stable. These molecules represent a particular case where a quite high (570 and 714 cm$^{-1}$ respectively) internal rotation barrier is combined with relatively a high $\rho$ value (close to 0.3) making analysis of the spectra rather delicate. The fits were performed using a version of RAM36 code\footnote{Ilyushin, V.V. et al;{\em J. Mol. Spectrosc.}~{\bf259}, (2010) 26} which includes the treatment of the nuclear quadrupole hyperfine structure. Ethanimine was detected already in ISM\footnote{Loomis, R. A.; {\em et al.} {\em ApJ. Lett.}~{\bf765},(2013) L9}, but the spectrosocpic analyses were limited to low K$_{a}$ values\footnote{Lovas, F. J.; {\em et al.} {\em J. Chem. Phys.}~{\bf72}, (1980) 4964}$^{,}$\footnote{Melli A.; {\em et al.} {\em ApJ}~{\bf855}, (2018) 123}. In the current study we significantly extend the rotational quantum number coverage for this molecule.\\ The spectroscopic results for both molecules and searches of methylimino-acetonitrile in ISM will be presented.\\ \em{This work was supported by the CNES and the Action sur Projets de l'INSU, PCMI.

SUBMILLIMETER WAVE SPECTROSCOPY AND ISM SEARCH FOR PROPIONIC ACID

Two compounds with a C$_{2}$H$_{4}$O$_{2}$ formula have been detected in the Interstellar Medium (ISM): acetic acid (CH$_{3}$CO$_{2}$H) and methyl formate (CH$_{3}$OC(O)H), the latter being thermodynamically less stable than the former but more abundant. Among the higher homologues with a C$_{3}$H$_{6}$O$_{2}$ formula where a hydrogen atom in C$_{2}$H$_{4}$O$_{2}$ has been replaced by a CH$_{3}$ group, two compounds have already been detected: ethyl formate (EtOC(O)H) and methyl acetate (CH$_{3}$OC(O)CH$_{3}$). The higher thermodynamic stability of another isomer, the propionic acid (EtCO$_{2}$H), pushed us to record its rotational spectrum, since this compound has a high probability of being present in the ISM. The methyl top internal rotation should be taken into account, therefore the analysis is performed using RAM36 code.\footnote{Ilyushin, V.V. et al;{\em J. Mol. Spectrosc.}~{\bf259}, (2010) 26} The spectroscopic results and its search in ISM will be presented.\\ \em{This work was supported by the CNES and the Action sur Projets de l'INSU, PCMI

THz and ft-ir study of 18-o isotopologues of sulfur dioxide: 32S16O18O and 32S18O2

Sulfur dioxide is a molecule that have a great interest in different domains: for atmospheric and planetology chemistry, it is also ubiquitous and abundant in interstellar medium. If the $^{16}$O species were extensively studied, this is not the case of the $^{18}$O isotopologues. The aim of this study is first to complete the rotational spectra of the ground state with these new measurements up to 1.5 THz, previous measurements are up to 1050 GHz for the $^{32}$S$^{16}$O$^{18}$O species\footnote{Belov, S. P.{\em et al.}, 1998, {\em J. Mol. Spectrosc.}~{\bf191}, 17}, and 145 GHz concerning the $^{32}$S$^{18}$O$_2$ species\footnote{Lindermayer, J.{\em et al.}, 1985, {\em J. Mol. Spectrosc.}~{\bf110}, 357}. The second part is making a global fit of the rotational and vibrational transitions for the excited vibrational states. For the $v_2$ band, we will complete the recent I.R. analysis\footnote{Gueye, F.{\em et al.} {\em Mol. Phys.}~{\bf in press}}. About the triad ($v_1, 2v_2, v_3$): $^{32}$S$^{18}$O$_2$ species was studied\footnote{Ulenikov, O. N.{\em et al.}, 2015, {\em JQSRT}~{\bf166}, 13}, but not the $^{32}$S$^{16}$O$^{18}$O one.\\ The FT-IR spectra were recorded on the AILES Beamline at Synchrotron SOLEIL using the Synchrotron light source, coupled to the Bruker IFS125HR Fourier transform spectrometer\footnote{Brubach, J.{\em et al.}, 2010, {\em AIP Conf. Proc.}~{\bf1214}, 81}. The THz spectra were obtained from 150 to 1500 GHz using the Lille's solid state spectrometer\footnote{Zakharenko, O.{\em et al.}, 2015, {\em J. Mol. Spectrosc.}~{\bf317}, 41}. The analysis is in progress, the latest results will be presented.\\ \em{Support from the French Laboratoire d'Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d'Investissements d'Avenir is acknowledged

MILLIMETER WAVE SPECTRUM OF METHYL KETENE AND ITS SEARCH IN ORION

The knowledge of synthetic routes of complex organic molecules is still far to be fully understood. The creation of reliable models is particularly challenging. Hollis et al.footnote{Hollis, J. M.; {em et al.}, 2006, {em ApJ}~{bf642}, 933} pointed out that the observations of molecular isomers provides an excellent tool to evaluate the hypothesis of the synthetic pathways. In the group of isomers chem{C_3H_4O} that contains two unsaturations, the three most stable are cyclopropanone, propenal (also known as acrolein) and methyl ketene. Among these isomers, only propenal was tentatively detected in Sgr B2(N)footnote{Hollis, J. M.; {em et al.}, 2006, {em ApJ}~{bf643}, L25}. Spectroscopic measurements of methyl ketene chem{CH_3CHCO} are limited to the microwave domainfootnote{Bak, B.; {em et al.}, 1966, {em J. Chez. Phys.}~{bf45}, 883}. We extended the measurements into millimeter waves in order to provide accurate frequency predictions suitable for astrophysical purposes. Methyl ketene has one more carbon atom than acetaldehyde (chem{CH_3CHO}) and in terms of rotational spectroscopy is quite similar to acetaldehyde. The analysis of the rotational spectrum of methyl ketene is complicated due to internal rotation of the methyl group, that is characterized by the barrier of intermediate height $V_3 =$ 416 wn, and by quite large value of the coupling parameter $rho = 0.194$. The spectroscopic results and the searches of methyl ketene in Orion will be presented. \_x000d_ em{This work was supported by the CNES and the Action sur Projets de l'INSU, PCMI. This work was also done under ANR-13-BS05-0008-02 IMOLABS

SPECTROSCOPY OF NEW IMINE ASTROPHYSCICS TARGET: METHYLIMINO-ACETONITRILE (CH3N=CHCN)

There are to date about 200 molecules that have been detected in the interstellar medium or circumstellar shells. Among these molecules, several tens are the methylated derivatives of compounds previously detected. For several years, we have been studying molecules belonging to the imine family. Following the detection of the dimer of HCN, the cynaoethanimine, its methylated derivative, methylimino-acetonitrile \ce{CH3N=CHCN} appears as a privileged target. Methylimino-acetonitrile has two isomers $E$ and $Z$. According to quantum chemical calculations, the $E$ isomer is more stable than $Z$ by about 1.5~kJ/mol. There was no spectrosocpic data allowing detection without ambiguity of this molecule in the interstellar medium. We recorded and analyzed the spectra of methylimino-acetonitrile up to 660~GHz. This compound is not stable in laboratory conditions, it was produced in-situ by pyrolisis and introduced in a 1~m long pyrex cell in a flow mode. The $E$ isomer represents an interesting case from spectroscopic point of view. Even if the barrier to internal rotation of the methyl top is quite high 714~\wn, some A-E tunneling splittings were observed. This is due to quite high $\rho$ value: 0.274, just slightly smaller than the acetaldehyde value of 0.329. The analysis is performed using the RAM36 code\footnote{Ilyushin, V.V. et al; {\em J. Mol. Spectrosc.}~{\bf259}, (2010) 26}. The spectroscopic results will be presented.\\ \\ \footnotesize{Acknowledgements: These results were supported by the Programme National PCMI of CNRS/INSU with INC/INP co- funded by CEA and CNES, the French National Research Agency (ANR-13-BS05-0008 ”IMOLABS”

Searching for Trans Ethyl Methyl Ether in Orion KL

We report on the tentative detection of $trans$ Ethyl Methyl Ether (tEME), $t-CH_3CH_2OCH_3$, through the identification of a large number of rotational lines from each one of the spin states of the molecule towards Orion KL. We also search for $gauche$-$trans$-n-propanol, $Gt-n-CH_3CH_2CH_2OH$, an isomer of tEME in the same source. We have identified lines of both species in the IRAM 30m line survey and in the ALMA Science Verification data. We have obtained ALMA maps to establish the spatial distribution of these species. Whereas tEME mainly arises from the compact ridge component of Orion, Gt-n-propanol appears at the emission peak of ethanol (south hot core). The derived column densities of these species at the location of their emission peaks are $\leq(4.0\pm0.8)\times10^{15} cm^{-2}$ and $\leq(1.0\pm0.2)\times10^{15} cm^{-2}$ for tEME and Gt-n-propanol, respectively. The rotational temperature is $\sim100 K$ for both molecules. We also provide maps of $CH_3OCOH$, $CH_3CH_2OCOH$, $CH_3OCH_3$, $CH_3OH$, and $CH_3CH_2OH$ to compare the distribution of these organic saturated O-bearing species containing methyl and ethyl groups in this region. Abundance ratios of related species and upper limits to the abundances of non-detected ethers are provided. We derive an abundance ratio $N(CH_3OCH_3)/N(tEME)\geq150$ in the compact ridge of Orion.Comment: Accepted in A&A Letter

SUBMILLIMETER WAVE INVESTIGATION OF TWO FORMAMIDE ISOMERS: FORMALDOXIME (CH2NOH) AND NITROSOMETHANE (CH3NO)

The knowledge of synthetic routes of complex organic molecules is still far to be fully understood. The creation of reliable models is particularly challenging. Hollis et al.\footnote{Hollis, J. M.; {\em et al.}, 2006, {\em ApJ}~{\bf 642}, 933} pointed out that the observations of molecular isomers provides an excellent tool to evaluate the hypothesis of the synthetic pathways. Formamide (HC(O)NH$_2$) is an abundant molecule in ISM detected in 1971 in SgrB2\footnote{Rubin, R. H. ; {\em et al.}, 1971, {\em ApJ}~{\bf 169}, L39}. Since formaldoxime and nitrosomethane are two isomers of formamide, they are interesting ISM targets. Up to now the spectroscopic studies are only available up to 40 GHz\footnote{Kaushik V. K. ; {\em et al.}, 1978, {\em J. Phys. Soc. Jap.}~{\bf 45}, 1975} \footnote{Turner P. H. {\em et al.}, 1978, {\em J. Chem. Soc., Faraday Trans. 2}~{\bf 74}, 533}. We reinvestigated the spectra of both isomers in the submillimeterwave domain in order to provide more accurate prediction to permit their possible detection in ISM. These two molecules are not commercially available and shoud be synthesized. The spectra were recorded in Lille from 150 to 660 GHz. In the region below 500 GHz we used the new Fourier transform millimeter-wave (FTmmW) spectrometer system based on DDS particulary suitable for unstable species\footnote{Zou L.; {\em et al.}, 2019, {\em 74$^{th}$ ISMS, Champaign USA}~{\bf FB04}}. Both analysis are not obvious, formaldoxime has a small dipole moment value: 0.2 Debye, giving weak transitions in the observed spectra. Concerning nitrosomethane, the methyl top internal rotation should be taken into account, therefore the analysis is performed using the version of RAM36 coded which includes the treatment of the nuclear quadrupole hyperfine structure\footnote{Ilyushin, V.V. {\em et al}, 2010, {\em J. Mol. Spectrosc.}~{\bf 259}, 26}. The first spectroscopic results will be presented. \em{This work was supported by the CNES and the Action sur Projets de l'INSU, PCMI.

THZ SPECTROSCOPY OF SULFUR DERIVATIVES OF ASTROPHYSICAL INTEREST

About 200 molecules have thus far been detected in the interstellar medium. Twenty-two are sulfur-bearing chemical compounds (and analogues of oxygenated species), making sulfur the tenth most abundant element in the galaxy. We report here the sub-THz spectroscopic observations of two reactive species: thioacetaldehyde (\chem{CH_3CHS}) and \chem{NS^+}.\footnote{Cernicharo J.; {\em et al.}, 2018, {\em ApJL}~{\bf L22}, 852} The latter new cation has been firmly detected for the first time towards many interstellar sources (cold molecular clouds, pre-stellar cores and shocks) using the IRAM-30m radiotelescope. Although a recent study of the chemistry of sulfur in cold dense clouds has been carried out \footnote{Fuente A.; {\em et al.} {\em A\&A}~{\bf 593}, (2016) A94} the formation pathways of the sulfur species are still misunderstood. \\ The rotational spectrum of \chem{CH_3CHS} was previously recorded up to 40~GHz.\footnote{H. Kroto; {\em et al.}, 1976, {\em J. Mol. Spectrosc.}~{\bf 62}, 346} New measurements performed up to 660~GHz represent a significant extension in terms of frequency range and analysis. The final spectroscopic analysis, including the internal rotation treatment, and searches for it towards SgrB2 and other sources will be presented. \\ \\ \footnotesize{Acknowledgements: These results were supported by the Programme National PCMI of CNRS/INSU, the French National Research Agency (ANR-13-BS05-0008 ”IMOLABS”), the CaPPA project (ANR-11-LABX-0005-01), the spanish MINECO (grants AYA2012-32032, AYA2016- 75066-C2-1-P, CSD2009-00038 and RyC-2014-16277) and the European Research Council (grant ERC- 2013-SyG 610256, NANOCOSMOS). Kharkov group acknowledge support of the Volkswagen foundation and assistance of the Science and Technology Center in Ukraine (STCU partner project P686).

SUBMILLIMETER WAVE SPECTRUM OF THIOACETALDEHYDE AND ITS SEARCH IN SgrB2

Sulfur chemistry in the interstellar medium is clearly misunderstood, the tenth most abundant element in the Galaxy, it is depleted in molecular clouds by a factor of 1000 footnote{A. Tieftrunk; {em et al.}, 1994, {em A&A}~{bf289}, 579}. This suggests that sulfur chemistry is important on icy grain mantles, and that sulfur-bearing molecules may be not detected yet due to the lack of laboratory data. The present study is about thioacetaldehyde (CH$_3$CHS), the analog of acetaldehyde._x000d_ Previously, the rotational spectra were recorded up to 40 GHz footnote{H. Kroto; {em et al.}, 1974, {em Chem. Phys. Lett.}~{bf29}, 265},footnote{H. Kroto; {em et al.}, 1976, {em J. Mol. Spectrosc.}~{bf62}, 346}. New spectra were recorded from 150 to 660 GHz using the Lille solid-state based spectrometer. The new fast version of the spectrometer using DDS component is particulary suitable for reactive species like thioacetaldehyde. Thioacetaldehyde was produced in-situ by pyrolisis at 750$^{circ} {rm C}$ and introduced in a 1m long pyrex cell in a flow mode. _x000d_ Analysis of the spectra is not obvious, like in acetaldehyde, as this molecule exhibits internal rotation of the methyl group. The internal rotation barrier is higher in thioacetaldehyde, 542 cm-1, than in acetaldehyde, 408 cm-1. However, the coupling between the internal rotation and the overall rotation in thioacetaldehyde is strong, the coupling parameter $rho$ value is 0.261 just slightly smaller than the acetaldehyde value of 0.329. The spectroscopic results and its searches in SgrB2 will be presented.\_x000d_ em{This work was supported by the CNES and the Action sur Projets de l'INSU, PCMI. This work was also done under ANR-13-BS05-0008-02 IMOLABS