arXiv subjects

Laurent Margulès

Publications and source records attributed to Laurent Margulès.

9 recordsLinked to original sources

arXiv2025

Rotational Spectroscopy and Tentative Interstellar Detection of 3-Hydroxypropanal (HOCH$_2$CH$_2$CHO) in the G+0.693-0.027 Molecular Cloud

We synthesized the astrochemically relevant molecule 3-hydroxypropanal (HOCH$_2$CH$_2$CHO) and subsequently measured and analyzed its rotational spectrum in several frequency regions ranging from 130 to 485 GHz. We analyzed the ground vibrational state as well as the two perturbed lowest-lying vibrationally excited states. With the resulting rotational parameters, we searched for this molecule in the Sagittarius B2(N) and NGC 6334I hot cores, the IRAS 16293-2422B hot corino, and the G+0.693-0.027 and TMC-1 molecular clouds. Rotational emission of 3-hydroxypropanal was tentatively detected toward G+0.693-0.027 and a column density of (8.6$\pm$1.4)$\times$10$^{12}$ cm$^{-2}$ was determined. However, this molecule was not detected in the other sources that were investigated. The chemical implications of this tentative discovery are analyzed and several potential chemical formation pathways of this species are discussed.

astro-ph.GA↗

arXiv2025

Evidence for electron spin-torsion coupling in the rotational spectrum of the CH$_3$CO radical

Open-shell non-rigid molecular systems exhibiting an internal rotation are likely candidates for a coupling between the spin angular momentum of the unpaired electron and the torsional motion. This electron spin-torsion coupling lacked both an experimental validation and a theoretical modeling. Here, the first experimental observation of the electron spin-torsion coupling is reported analyzing the pure rotational spectrum at millimeter wavelengths of the CH$_3$CO radical, a $^2Σ$ open-shell molecule displaying an internal rotation of its methyl group. To account for this coupling, a specific Hamiltonian incorporating the rotational, torsional, and electronic degrees of freedom is developed and allows us to reproduce the experimental spectrum. The present demonstration of the electron spin-torsion coupling will undoubtedly be key to future investigations of large open-shell molecules exhibiting a complex internal dynamics.

physics.chem-ph↗

arXiv2024

Rotational Spectrum and First Interstellar Detection of 2-Methoxyethanol Using ALMA Observations of NGC 6334I

We use both chirped-pulse Fourier transform and frequency modulated absorption spectroscopy to study the rotational spectrum of 2-methoxyethanol in several frequency regions ranging from 8.7-500 GHz. The resulting rotational parameters permitted a search for this molecule in Atacama Large Millimeter/submillimeter Array (ALMA) observations toward the massive protocluster NGC 6334I as well as source B of the low-mass protostellar system IRAS 16293-2422. 25 rotational transitions are observed in the ALMA Band 4 data toward NGC 6334I, resulting in the first interstellar detection of 2-methoxyethanol. A column density of $1.3_{-0.9}^{+1.4} \times 10^{17}$ cm$^{-2}$ is derived at an excitation temperature of $143_{-39}^{+31}$ K. However, molecular signal is not observed in the Band 7 data toward IRAS 16293-2422B and an upper limit column density of $2.5 \times 10^{15}$ cm$^{-2}$ is determined. Various possible formation pathways--including radical recombination and insertion reactions--are discussed. We also investigate physical differences between the two interstellar sources that could result in the observed abundance variations.

astro-ph.GA↗

arXiv2023

Millimeter-wave spectrum of 2-propanimine

Up to date, only 6 imines have been detected in the interstellar medium. The 3-carbon imine, 2-propanimine ((CH$_3$)$_2$C=NH), is predicted to be the structural isomer with the lowest energy in the C$_3$H$_7$N group, and appears to be a good candidate for astronomical searches. Unexpectedly, no microwave or millimeter wave spectrum is available for 2-propanimine. In this work, we provide the first high resolution millimeter wave spectrum of 2-propanimine and its analysis. With the guide of this laboratory measurement, we aim to search for 2-propanimine in two molecule-rich sources Sgr B2(N) and IRAS 16293-2422 using observations from the Atacama Large Millimeter/submillimeter Array (ALMA). Starting from a synthesized sample, we measured the spectrum of 2-propanimine from 50 to 500 GHz, and the ground state lines are successfully assigned and fitted using XIAM and ERHAM programs with the aid of theoretical calculations. The barriers to internal rotation of the two CH$_3$ tops are determined to be 531.956(64) cm$^{-1}$ and 465.013(26) cm$^{-1}$. These data are able to provide reliable prediction of transition frequencies for astronomical search. Although a few line matches exist, no confirmed detection of 2-propanimine has been found in the hot molecular core Sgr B2(N1S) and the Class 0 protostar IRAS 16293B. Upper-limits of its column density have been derived, and indicate that 2-propanimine is at least 18 times less abundant than methanimine in Sgr B2(N1S), and is at most 50-83 % of methanimine in IRAS 16293B.

astro-ph.GA↗

arXiv2022

Successive deuteration in low-mass star-forming regions: the case of D$_{2}$-methanol (CHD$_{2}$OH) in IRAS 16293-2422

Accurate quantification of the column density of di-deuterated methanol is a key missing puzzle piece in the otherwise thoroughly constrained family of D-bearing methanol in the deeply embedded low-mass protostellar system and astrochemical template source IRAS16293-2422. A spectroscopic dataset for astrophysical purposes is built for CHD$_{2}$OH and made publicly available to facilitate accurate characterization of this species in astrochemical surveys. The newly computed line list and partition function are used to search for CHD$_{2}$OH towards IRAS16293-2422 A and B in data from ALMA-PILS. Only non-blended, optically thin lines of CHD$_{2}$OH are used for the synthetic spectral fitting. The constructed spectroscopic database contains line frequencies and strengths for 7417 transitions in the 0 to 500 GHz frequency range. ALMA-PILS observations in the 329-363 GHz range are used to identify 105 unique, non-blended, optically thin line frequencies of CHD$_{2}$OH for synthetic spectral fitting. The derived excitation temperatures and column densities yield high D/H ratios of CHD$_{2}$OH in IRAS 16293-2422 A and B of 7.5$\pm$1.1% and 7.7$\pm$1.2%, respectively. Deuteration in IRAS 16293-2422 is not higher than in other low-mass star-forming regions. Di-deuterated molecules consistently have higher D/H ratios than their monodeuterated counterparts in all low-mass protostars, which may be a natural consequence of H-D substitution reactions as seen in laboratory experiments. The Solar System's natal cloud, as traced by comet 67P/Churyumov-Gerasimenko, may have had a lower initial abundance of D, been warmer than the cloud of IRAS16293-2422, or been partially reprocessed. In combination with accurate spectroscopy, a careful spectral analysis, and a consideration of the underlying assumptions, successive deuteration is a robust window on the physicochemical provenance of star-forming systems.

astro-ph.GA↗

arXiv2021

Deciphering the Rotational Spectrum of the First Excited Torsional State of Propylene Oxide

The first excited torsional state of the chiral molecule propylene oxide, $\mathrm{CH_{3}C_{2}H_{3}O}$, is investigated from millimeter up to sub-millimeter wavelengths (75-950 GHz). The first excited vibrational mode of propylene oxide, $\upsilon_{24}$, is analysed using the programs ERHAM and XIAM. Rotational constants and tunneling parameters are provided, and a description of the A-E splittings due to internal rotation is given. Furthermore, the potential barrier height to internal rotation $V_{3}$ is determined to be $V_{3} = 894.5079(259) \mathrm{cm^{-1}}$ . Our results are compared with quantum chemical calculations and literature values. We present a line list of the dense spectrum of the first excited torsional state of propylene oxide in the (sub-)millimeter range. Our results will be useful for further studies of chiral molecules in vibrationally excited states, and will enable astronomers to search for rotational transitions originating from $\upsilon_{24}$ of propylene oxide in interstellar space.

physics.chem-ph↗

arXiv2019

Characterising molecules for fundamental physics: an accurate spectroscopic model of methyltrioxorhenium derived from new infrared and millimetre-wave measurements

Precise spectroscopic analysis of polyatomic molecules enables many striking advances in physical chemistry and fundamental physics. We use several new high-resolution spectroscopic devices to improve our understanding of the rotational and rovibrational structure of methyltrioxorhenium (MTO), the achiral parent of a family of large oxorhenium compounds that are ideal candidate species for a planned measurement of parity violation in chiral molecules. Using millimetre-wave and infrared spectroscopy in a pulsed supersonic jet, a cryogenic buffer gas cell, and room temperature absorption cells, we probe the ground state and the Re=O antisymmetric and symmetric stretching excited states of both CH3 187 ReO3 and CH3 185 ReO3 isotopologues in the gas phase with unprecedented precision. By extending the rotational spectra to the 150-300 GHz range, we characterize the ground state rotational and hyperfine structure up to J = 43 and K = 41, resulting in refinements to the rotational, quartic and hyperfine parameters, and the determination of sextic parameters and a centrifugal distortion correction to the quadrupolar hyperfine constant. We obtain rovibrational data for temperatures between 6 and 300 K in the 970-1015 cm-1 range, at resolutions down to 8 MHz and accuracies of 30 MHz. We use these data to determine more precise excited-state rotational, Coriolis and quartic parameters, as well as the ground-state centrifugal distortion parameter D K of the 187 Re isotopologue. We also account for hyperfine structure in the rovibrational transitions and hence determine the upper state rhenium atom quadrupole coupling constant eQq' .

physics.atom-ph↗

arXiv2017

ALMA Detection of Interstellar Methoxymethanol (CH$_3$OCH$_2$OH)

We report the detection of interstellar methoxymethanol (CH$_3$OCH$_2$OH) in ALMA Bands 6 and 7 toward the MM1 core in the high-mass star-forming region NGC 6334I at ~0.1" - 1" spatial resolution. A column density of 4(2) x $10^{18}$ cm$^{-2}$ at $T_{ex}$ = 200 K is derived toward MM1, ~34 times less abundant than methanol (CH$_3$OH), and significantly higher than predicted by astrochemical models. Probable formation and destruction pathways are discussed, primarily through the reaction of the CH$_3$OH photodissociation products, the methoxy (CH$_3$O) and hydroxymethyl (CH$_2$OH) radicals. Finally, we comment on the implications of these mechanisms on gas-phase vs grain-surface routes operative in the region, and the possibility of electron-induced dissociation of CH$_3$OH rather than photodissociation.

astro-ph.GA↗

arXiv2008

Rotational spectrum of deuterated and 15N ethyl cyanides: CH3CHDCN and CH2DCH2CN and of CH3CH2C15N

Ethyl cyanide is an abundant molecule in hot molecular clouds. Lines from 13C isotopically substituted ethyl cyanide were identified in Orion. To enable the search and the possible detection of other isotopologues of ethyl cyanide in interstellar objects, we have studied the rotational spectrum of deuterated ethyl cyanide: CH2DCH2CN (in-plane and out-of-plane) and CH3CHDCN and the spectrum of15N substituted ethyl cyanide CH3CH2C15N. The rotational spectrum of each species in the ground state was measured in the microwave and millimeter-submillimeter wavelength range using a waveguide Fourier transform spectrometer (8 - 17 GHz) and a source-modulated spectrometer employing backward-wave oscillators (BWOs) (150 - 260 and 580 - 660 GHz). From the fitting procedure, accurate spectroscopic constants were derived for each of the species. These new sets of spectroscopic constants enable us to predict reliably the rotational spectrum (lines frequencies and intensities) in the 4-1000 GHz frequency range and for J and Ka up to 80 and 31, respectively. Combined with IRAM 30 m antenna observations of Orion, this experimental study allowed us to detect 15N substituted ethyl cyanide for the first time in Orion. The derived column density and rotational temperature are 10^13 cm-2 and 150 K for the plateau and 3 10^14 cm-2 and 300 K for the hot core. The deuterated species were searched for but were not detected. The upper limit to the column density of each deuterated isotopologues was 10^14 cm-2.

astro-ph↗