EXTENDED ANALYSIS OF THE ROTATIONAL SPECTRUM OF METHOXYISOCYANATE IN THE GROUND AND LOWEST EXCITED VIBRATIONAL STATES

Methoxyisocyanate, \chem{CH_3ONCO} is a methoxy derivative of isocyanic acid HNCO detected in the interstellar medium back in 1972\footnote{Snyder, L.E. and Buhl, D. 1972, $ApJ$, \textbf{177}, 619}. Recent detections of methyl isocyanate, a methyl derivative of HNCO, towards Sgr B2(N)\footnote{Halfen, D.T., Ilyushin, V.V. and Ziurys, L.M. 2015, $ApJ$, \textbf{812}, L5}, and in the Orion\footnote{Cernicharo, J. et al. 2016, \textit{A\&A}, \textbf{587}, L4}, as well as the detection of methoxymethanol\footnote{McGuire, B.M. 2017, $ApJ$ \textbf{851}, L46 (2017)} motivated us to study the rotational spectrum of \chem{CH_3ONCO} as a candidate molecule for searches in the interstellar medium. The previously presented study of the rotational spectrum of methoxyisocyanate\footnote{Pienkina, A. et al. 2017, 72nd ISMS, WA03} showed the complexity of the problem owing to the large amplitude motion, a skeletal torsion along ON bond. The analysis revealed the existence of the "ladder" Coriolis-type interactions between the ground and lowest skeletal torsional states. We present here the extension of the rotational spectrum analysis that includes new types of resonances as well as the assignment of new excited vibrational states of methoxyisocyanate. In particular, the inclusion of new resonances permitted to assign and fit within experimental accuracy high $K_a$ transitions of the ground vibrational state. \emph{This work was supported by the CNES and the Action sur Projets de l’INSU, PCMI.

FOURIER TRANSFORM MILLIMETER-WAVE SPECTROMETER WITH ORIGINAL DESIGN

Direct digital synthesizers (DDS) have a number of advantages, especially such as the high precision and rate of frequency adjustment. In addition, these synthesizers possess a unique property to allow changing the frequency from one value to another with continuous phase. Few years ago, we built fast-scan absorption spectrometer with Schottky diode frequency multiplication chains as a radiation source.\footnote{A. Pienkina, R.A. Motiyenko, L. Margul\`{e}s et al. ISMS, 71st symposium (2016), FB05} The rapid frequency scan in the spectrometer is provided by RF synthesizer based on up-conversion of the DDS signal. Owing to the capability of fast frequency switching, the same up-converted RF synthesizer may generate short pulses to polarize molecules and subsequently may be used as a local oscillator in the heterodyne detection of free induction decay. This feature simplifies the spectrometer design, as it allows using only one radiation source to polarize molecular sample, and to detect molecular signal. Using this principle, we built a Fourier transform spectrometer in the millimeter wave range. The spectrometer covers the frequency range between 150 and 220~GHz. In the current design, the RF synthesizer allows generation of frequency pulses with a bandwidth inverse proportional to pulse duration, as well as chirped pulses with a bandwidth of about 350~MHz. The performances of the spectrometer will be presented and discussed

ROTATIONAL SPECTROSCOPY OF 4-HYDROXY-2-BUTYNENITRILE

Recently we studied the rotational spectrum of hydroxyacetonitrile (HOCH$_2$CN, HAN) in order to provide a firm basis for its possible detection in the interstellar mediumfootnote{Margul`es L., Motiyenko R.A., Guillemin J.-C. textit{68th ISMS}, textbf{2013}, TI12.}. Different plausible pathways of the formation of HAN in the interstellar conditions were proposed;footnote{Danger G. et al. textit{Phys. Chem. Chem. Phys.} textbf{2014}, 16, 3360.} however, up to now, the searches for this molecule were unsuccessful. To continue the study of nitriles that represent an astrophysical interest we present in this talk the analysis of the rotational spectrum of 4-hydroxy-2-butynenitrile (HOCH$_2$CC-CN, HBN), the next molecule in the series of hydroxymethyl nitriles. Using the Lille spectrometer the spectrum of HBN was measured in the frequency range 50 -- 500 GHz. From the spectroscopic point of view HBN molecule is rather similar to HAN, because of -OH group tunnelling in textit{gauche} conformation. As it was previously observed for HAN, due to this large amplitude motion, the splittings in the rotational spectra of HBN are easily resolved making the spectral analysis more difficult. Additional difficulties arise from the near symmetric top character of HBN ($kappa = -0.996$), and very dense spectrum because of relatively small values of rotational constants and a number of low-lying excited vibrational states. The analysis carried out in the frame of reduced axis system approach of Pickettfootnote{Pickett H.M. textit{J. Chem. Phys.} textbf{1972}, 56, 1715.} allows to fit within experimental accuracy all the rotational transitions in the ground vibrational state. Thus, the results of the present study provide a reliable catalog of frequency predictions for HBN. \ em{The support of the Action sur Projets de l�INSU PCMI, and ANR-13-BS05-0008-02 IMOLABS is gratefully acknowledged

INTERNAL ROTATION ANALYSIS OF THE FTMW AND MILLIMETER WAVE SPECTRA OF FLUORAL (CF3CHO)

To protect atmosphere, hydrofluorocarbons (HFCs) are the current substituents of the dangerous CFCs and other ODS (ozone depleting substances).\footnote{Burkholder J.B. {\em et al.}, Chem.Rev., 2015,~{\bf115}, 3704} Although HFCs are not ODS, they are potent greenhouse gases and, thus, they would be harmful to climate. Consequently, there is a keen interest on monitoring their reaction and the decomposition products in order to measure their effects. Fluoral (trifluoroacetaldehyde, \ce{CF3CHO}) is one of the stable decomposition products of several families of ODS substituents. Monitoring it in the atmosphere is hampered by the few spectroscopic data available in the literature. The rotational spectrum of fluoral from 8-40~GHz was measured previously,\footnote{Woods R.C., 1967, J. Chem. Phys.,~{\bf46}, 4789} however the performed analysis of the spectrum was rather limited due to difficulties in theoretical description. These difficulties reside mainly in the hindered internal rotation of the \ce{CF3} group. Compared to acetaldehyde, in fluoral, the \ce{CF3} group represents the major part of the molecular mass. Therefore, there is a strong coupling between the overall molecular rotation and the internal rotation of the top $\rho=0.92$. As such, previously used principal axis method, where the axes remain unaffected by the large amplitude motion, is not fully suitable for the analysis. We present the analysis of new high resolution microwave and millimeter wave spectra of fluoral in the ranges 6-26 and 50-305~GHz, respectively, employing rho-axis method implemented in RAM36 program. The rotational distortional and internal rotational parameters that reproduce the spectral at experimental accuracy were determined for the ground state and several lowest excited torsional states

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

Rotational spectroscopy of malononitrile and its corresponding monoisocyanide isomer, isocyanoacetonitrile

International audienceContext. Nitrites constitute almost 20% of the molecules observed in the interstellar medium, whereas only one dinitrile and one isocyanonitrile compound have been detected up to now. The lack of detections of such compounds may be partially explained by the lack of accurate spectroscopic data on their rotational spectra. Aims. Two small seven-atom dinitriles, malononitrile NCCH2CN and isocyanoacetonitrile NCCH2NC, were chosen as target species for this study. For malononitrile the goal of the study is to systematize all the previous measurements, and to extend the measurements to the sub-millimeter wavelength range. The spectrum of isocyanoacetonitrile has not been studied before. Methods. The rotational spectra of the two molecules were measured in the frequency range 150-660 GHz using the Lille fast-scan spectrometer. The spectroscopic study was supported by high-level theoretical calculations on the structure of these molecules and their harmonic force field. Results. Accurate frequency predictions for malononitrile and isocyanoacetonitrile were calculated on the basis of the analysis of their rotational spectra. The influence of the spin statistics on the intensities of the lines of malononitrile was taken into account. The provided line lists and sets of molecular parameters meet the needs of astrophysical searches for the two molecules

Numerical Simulation of the Flow Inside a Scroll Compressor Equipped with Intermediate Discharge Valves

This paper presents the results of CFD simulations of the compression process of a scroll compressor. The compressor geometry accounts for the final scroll gas pockets, two Intermediate Discharge Valves (IDVs), the central discharge zone and the upper shell. The numerical model uses a real gas equation of state to determine gas properties during the compression process and accounts for the motion of the orbiting scroll and IDVs using a mesh smoothing and remeshing algorithm. The IDVs are represented as a spring mass system with their movement controlled via the pressure difference around the valve. Appropriate pressure based boundary conditions are used at entry to the third gas pocket and at the exit of the upper shell. An initial analysis of the results has shown that it is possible to achieve time accurate results of the pressure field throughout the flow domain and also determine the impact of the IDVs on scroll performance. The results will also enable a more thorough analysis of the fluid flow and compression process inside the scroll in order to improve its performance