The Rotational Spectrum of the β-Cyanovinyl Radical: A Possible Astrophysical N-Heterocycle Precursor

International audienceA fundamental question in the field of astro-chemistry is whether the molecules essential to life originated in the interstellar medium (ISM) and, if so, how they were formed. Nitrogen-containing heterocycles are of particular interest because of their role in biology, but to date no N-heterocycle has been detected in the ISM and it is unclear how and where such species might form. Recently, the β-cyanovinyl radical (HCCHCN) was implicated in the low temperature gas-phase formation of pyridine. While neutral vinyl cyanide (H 2 CCHCN) has been rotationally characterized and detected in the ISM, HCCHCN has not. Here we present the first theoretical study of all three cyanovinyl isomers at the CCSD(T)/ANO1 level of theory and the experimental rotational spectra of cis-and trans-HCCHCN, as well as those of their 15 N isotopologues, from 5 to 75 GHz. The observed spectra are in good agreement with calculations , and provide a basis for further laboratory and astronomical investigations of these radicals

HIGH RESOLUTION FAR INFRARED FOURIER TRANSFORM SPECTROSCOPY OF THE NH2_2 RADICAL.

Author Institution: SOLEIL Synchrotron, AILES beamline, Saint-Aubin, France and Institut des Sciences Moleculaires d'Orsay, ISMO, CNRS, Universite Paris XI, Orsay, France; SOLEIL Synchrotron, AILES beamline, Saint-Aubin, FranceFirst identified toward Sgr B2}, the NH$_2$ radical has recently been detected in the interstellar medium by the HIFI instrument on board of Herschel}. Despite the fact that this radical has not been detected in brown dwarfs and exoplanets yet, it is already included in physical and chemical models of those environments} (temperature higher than 2000 K expected in several objects). Its detection in those objects will depend on the existence of a reliable high temperature and high resolution spectroscopic database on the NH$_2$ radical.The absorption spectrum of NH$_2$ has been recorded between 15 and 700 cm$^{-1}$ at the highest resolution available using the Bruker IFS125HR Fourier transform interferometer connected to the far infrared AILES beamline at SOLEIL (R=0.001~cm$^{-1}$). The radical was produced by an electrical discharge (DC) through a continuous flow of NH$_3$ and He using the White-type discharge cell developped on the beamline (optical path: 24m). Thanks to the brilliance of the synchrotron radiation, more than 700 pure rotational transitions of NH$_2$ have been identified with high N values (N$_{max}$=25) in its fundamental and first excited vibrational modes. By comparison to the previous FT spectroscopic study on that radical in the FIR spectral range}, asymmetric splitting as well as fine and hyperfine structure have been resolved for several transitions

TERAHERTZ ROTATIONAL SPECTROSCOPY OF THE SO RADICAL

Author Institution: Laboratoire de Physico-Chimie de l'Atmosphere, EA 4493, Universite du Littoral Cote d'Opale, 59140 Dunkerque, France; Institut des Sciences Moleculaires d'Orsay, CNRS, UMR 8214, Universite Paris XI, bat. 210, 91405 Orsay Cedex, France; SOLEIL Synchrotron, AILES beamline, L'orme des Merisiers, Saint-Aubin, 91192 Gif-Sur-Yvette, FranceSulfur monoxide SO (X$^3\Sigma^-$) is a well-known interstellar radical identified in a wide variety of astrophysical environments 184, L59 (1973)} which is particularly abundant in star forming regions, \textit{Astrophys. J.} 315, 621 (1987)}. Due to its high reactivity and its role in chemical reactions involving O and S atoms, SO is also a reaction intermediate in combustion processes and chemistry of the Earth atmosphere, \textit{J. Mol. Spectrosc.} 124, 379 (1987)}. %The pure rotational spectrum of SO has been extensively studied in the laboratory from sub-millimeter to THz wavelength, \textit{J. Mol. Speectrosc.} 182, 85 (1997)}. However no far infrared (FIR) broadband investigation on this radical has been reported up to date, and several rotational transitions belonging to the spectral windows of the HIFI instrument (on board of the Herschel satellite) require accurate laboratory measurements. %\vspace{1em} We have recorded pure rotational transitions of SO in the THz spectral range using synchrotron-based Fourier-Transform (FT) FIR and continous wave (CW) THz techniques. A FT-FIR spectrum of SO has been recorded at the AILES beamline of SOLEIL synchrotron in the spectral range 44--93 \wn~using a resolution of 0.001~\wn~allowing an accuracy on line position of 0.00007~\wn~($\sim$ 2 MHz). A multipass absorption discharge cell aligned to an absorption path length of 24 m has been used, \textit{Rev. Sci. Instrum.} 82, 113106 (2011)}. A continuous electrical discharge (1~A / 980~V) in a flowing mixture of H$_2$S, He, H$_2$ and air (respectively at pressure of 0.01, 1.15, 0.14 and 0.06~mbar) was used to produce SO. On this spectrum, 102 transitions of SO have been identified with $N=31$ to $65$. Among the observed lines, 99 are detected for the first time (22 new transitions belong to the HIFI spectral windows). Due to our limited instrumental resolution, transitions involving $N$ ranging from $31$ to $43$ show unresolved fine structure triplets. Recently, in order to observe all fine structure components in the HIFI spectral windows, we have recorded a high resolution CW-THz spectrum of SO, \textit{J. Mol. Struct.} 1006, 13 (2011)}. At the time of the writing, this spectrum was under analysis

Terahertz spectroscopy of hydrogen sulfide

Pure rotational transitions of hydrogen sulfide (H2S) in its ground and first excited vibrational states have been recorded at room temperature. The spectrum comprises an average of 1020 scans at 0.005 cm−1 resolution recorded in the region 45–360 cm−1 (1.4 to 10.5 THz) with a globar continuum source using a Fourier transform spectrometer located at the AILES beamline of the SOLEIL synchrotron. Over 2400 rotational lines have been detected belonging to ground vibrational state transitions of the four isotopologues H232S, H233S, H234S, and H236S observed in natural abundance. 65% of these lines are recorded and assigned for the first time, sampling levels as high as J=26 and Ka=17 for H232S. 320 pure rotational transitions of H232S in its first excited bending vibrational state are recorded and analysed for the first time and 86 transitions for H234S, where some of these transitions belong to new experimental energy levels. Rotational constants have been fitted for all the isotopologues in both vibrational states using a standard effective Hamiltonian approach. Comprehensive comparisons are made with previously available data as well as the data available in HITRAN, CDMS, and JPL databases. The 91 transitions assigned to H236S give the first proper characterization of its pure rotational spectrum

HIGH RESOLUTION THZ AND FIR SPECTROSCOPY OF SOCl2_2

Author Institution: Laboratoire de Physico-Chimie de l'Atmosphere, EA 4493, Universite du Littoral Cote d'Opale, 59140 Dunkerque, France; Institut des Sciences Moleculaires d'Orsay, CNRS, UMR 8214, Universite Paris XI, bat. 210, 91405 Orsay Cedex, France; SOLEIL Synchrotron, AILES beamline, L'orme des Merisiers, Saint-Aubin, 91192 Gif-Sur-Yvette, FranceThionyl chloride (SOCl$_2$) is an extremely powerful oxidant widely used in industrial processes and playing a role in the chemistry of the atmosphere, \textit{J. Phys. Chem. A} 107, 6183 (2003)}. In addition, it has a molecular configuration similar to that of phosgene (COCl$_2$), and is therefore of particular interest for security and defense applications. Low resolution vibrational spectra of gas phase SOCl$_2$ 22,1193 (1954)} as well as high resolution pure rotational transitions up to 25 GHz 90, 3473 (1994)} have previously been investigated. To date no high resolution data are reported at frequencies higher than 25 GHz. \vspace{1em} We have investigated the THz absorption spectrum of SOCl$_2$ in the spectral region 70--650 GHz using a frequency multiplier chain coupled to a 1 m long single path cell containing a pressure of about 15 $\mu$bar. At the time of the writing, about 8000 pure rotational transitions of SO$^{35}$Cl$_2$ with highest $J$ and $K_a$ values of 110 and 50 respectively have been assigned on the spectrum. We have also recorded the high resolution FIR spectra of SOCl$_2$ in the spectral range 50--700 \wn~using synchrotron radiation at the AILES beamline of SOLEIL facility. A White-type cell aligned with an absorption path length of 150 m has been used to record, at a resolution of 0.001 \wn,~two spectra at pressures of 5 and 56 $\mu$bar of SOCl$_2$. On these spectra all FIR modes of SOCl$_2$ are observed ($\nu_2$ to $\nu_6$) and present a resolved rotational structure. Their analysis is in progress

Discovery of SiCSi in IRC+10216: A missing link between gas and dust carriers of SiC bonds

We report the discovery in space of a disilicon species, SiCSi, from observations between 80 and 350 GHz with the IRAM 30m radio telescope. Owing to the close coordination between laboratory experiments and astrophysics, 112 lines have now been detected in the carbon-rich star CWLeo. The derived frequencies yield improved rotational and centrifugal distortion constants up to sixth order. From the line profiles and interferometric maps with the Submillimeter Array, the bulk of the SiCSi emis- sion arises from a region of 6 arcseconds in radius. The derived abundance is comparable to that of SiC2. As expected from chemical equilibrium calculations, SiCSi and SiC2 are the most abundant species harboring a SiC bond in the dust formation zone and certainly both play a key role in the formation of SiC dust grains.Comment: To be published in the Astrophysical Journal Letters; Accepted May 6 201

First detection of NHD and ND2_2 in the interstellar medium

Deuterium fractionation processes in the interstellar medium (ISM) have been shown to be highly efficient in the family of nitrogen hydrides. To date, observations were limited to ammonia (NH$_2$D, NHD$_2$, ND$_3$) and imidogen radical (ND) isotopologues. We want to explore the high frequency windows offered by the \emph{Herschel Space Observatory} to search for deuterated forms of amidogen radical NH$_2$ and to compare the observations against the predictions of our comprehensive gas-grain chemical model. Making use of the new molecular spectroscopy data recently obtained at high frequencies for NHD and ND$_2$, both isotopologues have been searched for in the spectral survey towards the class 0 IRAS 16293-2422, a source in which NH$_3$, NH and their deuterated variants have been previously detected. We used the observations carried out with HIFI (Heterodyne Instrument for the Far Infrared) in the framework of the key program "Chemical Herschel surveys of star forming regions" (CHESS). We report the first detection of interstellar NHD and ND$_2$. Both species are observed in absorption against the continuum of the protostar. From the analysis of their hyperfine structure, accurate excitation temperature and column density values have been determined. The latter were combined with the column density of the parent species NH$_2$ to derive the deuterium fractionation in amidogen. The amidogen D/H ratio measured in the low-mass protostar IRAS 16293-2422 is comparable to the one derived for the related species imidogen and much higher than that observed for ammonia. Additional observations of these species will give more insights into the mechanism of ammonia formation and deuteration in the ISM. We finally indicate the current possibilities to further explore these species at submillimeter wavelengths.Comment: 11 pages, 5 figures, 7 tables. Accepted for publication in A&

Broadband terahertz heterodyne spectrometer exploiting synchrotron radiation at megahertz resolution

International audienceA new spectrometer allowing both high resolution and broadband coverage in the terahertz (THz) domain is proposed. This instrument exploits the heterodyne technique between broadband synchrotron radiation and a quantum cascade laser (QCL) based molecular THz laser that acts as the local oscillator (LO). Proof of principle for exploitation for spectroscopy is provided by the recording of molecular absorptions of hydrogen sulfide (H 2 S) and methanol (CH 3 OH) around 1.073 THz. Ultimately, the spectrometer will enable to cover the 1-4 THz region in 5 GHz windows at Doppler resolution

The molecular structure of gauche-1,3-butadiene: Experimental proof of non-planarity

International audienceThe planarity of the second stable conformer of 1,3-butadiene-the archetypal diene for the Diels-Alder reaction, in which a planar conjugated diene and a dienophile combine to form a ring-is not established. The most recent high level calculations predict the species to adopt a twisted, gauche structure due to steric interactions between the inner terminal hydrogens rather than a planar, cis structure favored by the conjugation of the doubled bonds. Here we unambiguously prove experimentally that the structure cis-1,3-butadiene is indeed gauche with a substantial dihedral angle of 34° , in excellent agreement with theory. Observation of two tunneling components indicates that the molecule undergoes facile interconversion between two equivalent enantiomeric forms. Comparison of experimentally determined structures for gauche-and trans-butadiene provides an opportunity to examine the effects of conjugation and steric interactions