LASER ABLATION OF SOLID ORGANIC PRECURSORS AS AN ALTERNATIVE TOOL IN THE GENERATION OF INTERSTELLAR MOLECULES

In the course of the investigation of the rotational spectrum of prebiotic hydantoic acid by Fourier transform microwave spectroscopy coupled to a laser ablation source in a supersonic expansion, rotational signatures of two cyclic molecules, hydantoin and 2,5-oxazolidinedione, have been unexpectedly observed along with the four most stable conformers of hydantoic acid.\footnote{Kolesniková, L.; León, I.; Alonso, E. R. et al.: \textit{J. Phys. Chem. Lett.} \textbf{2019}, accepted, DOI: 10.1021/acs.jpclett.9b00208.} Interestingly, two of them presented folded geometric arrangements that might act as precursors in the cyclization reactions assisted by laser ablation. They could play the role of near-attack conformations (NACs) in the framework of the NAC theory for intramolecular reactions. A detailed analysis of the spectrum further revealed the simultaneous formation of other species in the jet, showing that the laser ablation of solid organic precursors constitutes an alternative tool in the generation of new chemical species.$^{b}$ It has been recently confirmed using diaminomaleonitrile as a solid precursor. Up to 30 different species (most of them detected in space) have been revealed in the supersonic expansion of our laser ablation chirped pulse Fourier transform microwave LA-CP-FTMW experiment

THE LABORATORY ROTATIONAL STUDY OF METHYL ISOCYNATE

Methyl isocyanate (CH$_{3}$NCO) is one of the most abundant species detected on the surface of the 67P/Churyumov-Gerasimenko comet.\footnote{Goesmann, F., Rosenbauer, H., Bredehoft, J.H., et al. 2015, Science, 349, aab0689.} It has also been discovered in space towards the Orion clouds where a large number of rotational lines arising from energy levels with $K \leq 3$ were reported.\footnote{Cernicharo, J., Kisiel, Z., Tercero, B., et al. 2016, A\&A, 587, L4.} In the present work, Stark-modulation spectroscopy was used to record the room temperature rotational spectrum of CH$_{3}$NCO in the spectral region from 32 to 90 GHz and to assign rotational transitions up to $K$ = 10. These new assignments were subsequently followed up to 364 GHz. Also, first laboratory measurements between 50 and 300 GHz have been performed for CH$_{3}$N$^{13}$CO and $^{13}$CH$_{3}$NCO isotopologues. Updated extensive line lists along with new sets of spectroscopic parameters provided in this work meet the needs for further detections of CH$_{3}$NCO in space

THE CONFORMATIONAL PANORAMA OF MANDELIC ACID

The conformational landscape of mandelic acid (phenyl glycolic acid), the simplest alpha-hydroxy acid containing an aromatic substituent, has been unveiled by laser ablation coupled with broadband Fourier transform microwave spectroscopy LA-CP-FTMW. The four identified conformers provide the first global structural picture of this molecule traditionally used in cosmetics and dermatology as well as in the synthesis of pharmaceuticals. Rotational transitions of singly substituted $^{13}$C isotopic species of the most stable conformer in its natural abundances were also detected, providing insight on its geometry

LASER ABLATION OF SOLID ORGANIC PRECURSORS: AN INNOVATIVE APPROACH FOR THE LABORATORY GENERATION OF CHEMICAL SPECIES

The high amount of reactive species participating in the chemistry in the Earth$^{'}$s upper atmosphere, interstellar medium, or combustion processes motivates laboratory experimentalists to develop efficient methods for the molecular \textit{in situ} generations to characterize these species spectroscopically. In the present contribution, we propose a new approach based on the laser ablation of solid organic compounds. A proof-of-concept experiment is performed using diaminomaleonitrile and uridine as prototypical precursors. Once formed in the throat of our laser ablation source, the products are entrained in the carrier gas, stabilized in the cold environment of the supersonic expansion, and are monitored by high-resolution chirped pulse Fourier transform microwave spectroscopy. We experimentally demonstrate a simultaneous formation of an impressive number and variety of species, both known and unknown. With these inspiring achievements in hands, we extend the boundaries for the molecular \textit{in situ} generations beyond traditional techniques such as electric discharge and pyrolysis

The Millimeter-wave Spectrum Of Vinyl Acetate

Recent discovery of methyl acetate in Orion KL\footnote{B.~Tercero, I.~Kleiner, J.~Cernicharo, H.~V.~L. Nguyen, A.~L\'{o}pez, and G.~M.~Mu\~{n}oz Caro, \textit{Astrophys. J. Lett.} \textbf{2013}, \textit{770}, 13.} places the vinyl acetate as a potential candidate possibly present in the interstellar medium. The room-temperature rotational spectrum of vinyl acetate has been measured from 125 up to 360~GHz to provide direct frequencies to the astronomical community. Transition lines, corresponding to the most stable conformer, have been observed and assigned on the basis of the previously determined spectroscopic constants.\footnote{B.~Velino, A.~Maris, S.~Melandri, W.~Caminati, \textit{J. Mol. Specrosc.} \textbf{2009}, \textit{256}, 228.} All the rotational transitions reveal the $A-E$ splitting due to the methyl internal rotation and the precise set of the spectroscopic constants obtained from the least-squares fit to a threefold barrier internal rotation Hamiltonian is reported. Additional measurements have been also made using a broadband CP-FTMW spectrometer in the region of $6–18$~GHz which made possible to assign all monosubstituted $^{13}$C and $^{18}$O isotopic species in natural abundance and to derive the molecular structure

Cis-methyl Vinyl Ether: The Rotational Spectrum Up To 600 Ghz

Astronomical observation of dimethyl ether,\footnote{Z.~Peeters, S.~D.~Rodgers, S.~B.~Charnley, L.~Schriver-Mazzuoli, A.~Schriver, J.~V.~Keane, and P.~Ehrenfreund, \textit{Astron. \& Astrophys.} \textbf{2006}, \textit{445}, 197.} methyl ethyl ether\footnote{G.~W.~Fuchs, U.~Fuchs, T.~F.~Giesen, F.~Wyrowski, \textit{Astron. \& Astrophys.} \textbf{2005}, \textit{444}, 521.} and vinyl alcohol\footnote{B.~E.~Turner, A.~J.~Apponi, \textit{Astrophys. J. Lett.} \textbf{2001}, \textit{561}, 207.} places the methyl vinyl ether among the species of potential interstellar relevance. The millimeter and submillimeter-wave transitions pertaining to the vibrational ground state and the first excited states of the methoxy, $\nu_{24}$, and methyl, $\nu_{23}$, torsional modes and the in-plane bending mode, $\nu_{16}$, of the \textit{cis}-methyl vinyl ether have been measured and analyzed in the frequency region from 50 to 600~GHz. A significant Fermi-type and Coriolis interactions between the $v_{24}=1$ and $v_{23}=1$ states have been observed and the rotational spectra were analyzed using an effective two-state Hamiltonian explicitly involving corresponding coupling operators. A sets of spectroscopic constants for the ground state as well as for all three excited states reproducing the observed spectrum within the experimental uncertainty provide sufficiently precise information for the astronomical search for methyl vinyl ether

Spectroscopic Characterization And Detection Of Ethyl Mercaptan In Orion

The rotational spectrum of ethyl mercaptan, CH$_{3}$CH$_{2}$SH, has been measured in the microwave, millimeter- and submillimeter-wave regions from 8 to 880 GHz and more than 2800 distinct transition frequencies have been assigned for the $gauche$- and $trans$-conformers. Very precise values of the spectroscopic constants allowed the detection of the $gauche$-CH$_3$CH$_2$SH towards Orion KL.\footnote{L.~Kolesnikov\'{a}, B.~Tercero, J.~Cernicharo, A.~M.~Daly, J.~L.~Alonso, B.~P.~Gordon, S.~Shipman, \textit{Astrophys. J. Lett.} \textbf{2014}, accepted.} 77 unblended or slightly blended lines plus no missing transitions in the range 80~--~280~GHz support this identification. $Trans$--CH$_3$CH$_2$SH has been detected tentatively

Laboratory Detection of Cyanoacetic Acid: A Jet-Cooled Rotational Study

Herein we present a laboratory rotational study of cyanoacetic acid (CH2(CN)C(O)OH), an organic acid as well as a -CN bearing molecule, that is a candidate molecular system to be detected in the interstellar medium (ISM). Our investigation aims to provide direct experimental frequencies of cyanoacetic acid to guide its eventual astronomical search in low-frequency surveys. Using different jet-cooled rotational spectroscopic techniques in the time domain, we have determined a precise set of the relevant rotational spectroscopic constants, including the 14N nuclear quadrupole coupling constants for the two distinct structures, cis- and gauche- cyanoacetic acid. We believe this work will potentially allow the detection of cyanoacetic acid in the interstellar medium, whose rotational features have remained unknown until now.The authors thank the financial funding from Ministerio de Ciencia e Innovación (CTQ2016-76393-P and PID2019-111396GB-I00), Junta de Castilla y Leon (VA077U16 and VA244P20), and European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC-2013-SyG, grant agreement No. 610256 NANOCOSMOS. E.R.A. thanks Ministerio de Ciencia, Innovacion y Universidades for Juan de la Cierva grant (FJC2018-037320-I). M.S.N. acknowledges funding from the Spanish "Ministerio de Ciencia, Innovacion y Universidades" under predoctoral FPU Grant (FPU17/02987).Peer reviewe

Rotational Fingerprints of Vinylketene for Astronomical Observations

A high degree of isomerism in the realm of interstellar molecules stimulates systematic astronomical investigations of members of different families of isomers. Among them, vinyl-bearing compounds have kindled considerable interest due to recent detections of vinylamine, vinylacetylene, and vinylcyanoacetylene. Herein, we open the possibility to search for vinylketene in the interstellar space by means of its rotational transitions. The pure rotational spectrum of the title molecule was recorded in the frequency regions 195–218 and 293–324 GHz and an improved and extended set of spectroscopic parameters has been obtained for the most stable trans conformer. In addition, rotational signatures and molecular constants for the less stable cis form are reported for the first time. We provide a catalog of precise transition frequencies and intensities of vinylketene to the astronomical community and pave the way toward interstellar explorations of C _4 H _4 O isomer family