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Context. Substituted methanimines and ethylenes have been identified in the interstellar medium. Therefore, allylimine (CH2 =CH–CH=NH) represents a promising candidate for a new interstellar detection. Aims. The goal of the present work is to perform a comprehensive laboratory investigation of the rotational spectrum of allylimine in its ground vibrational state in order to obtain a highly precise set of rest frequencies to assist its search for astronomical sources. Methods. The rotational spectra of the two most stable trans–anti and trans–syn geometrical isomers of allylimine were recorded in the laboratory in the 84–300 GHz frequency interval. Measurements were performed using a source-modulation millimetre-wave spectrometer equipped with a pyrolysis system for the production of unstable species. High-level ab initio calculations were performed to assist the analysis and to obtain reliable estimates for an extended set of spectroscopic parameters. Guided by new laboratory data, allylimine was searched for in space using a sensitive spectral survey of the G+0.693-0.027 molecular cloud, located at the Galactic centre. Results. Almost 1000 rotational transitions have been recorded for trans–anti and trans–syn allylimine. These new data have enabled the determination of a very accurate set of spectroscopic parameters including rotational, quartic and sextic centrifugal distortion con-stants, as well as nuclear quadrupole coupling constants. The improved spectral data allowed us to report a tentative detection for both allylimine isomers in the G+0.693-0.027 molecular cloud, located at the Galactic centre.

The far-infrared spectrum of HC3N has been recorded at high resolution between 70 and 500 cm−1using synchrotron radiation. Four prominent features, i.e., ν7, ν6−ν7, ν4−ν6, and 2ν7 have been identified in the spectrum together with many associated hot bands. In addition, rotational transitions for the interacting v4=v7=1, (v6=2,v7=1), (v5=1,v7=2), and v7=5 vibrationally excited states have been recorded in the millimeter/submillimeter region. The newly assigned transitions, together with those reported previously, form a comprehensive data set including about 17 000 transitions, which involves almost all the vibrational states of HC3N lying below 1300 cm−1 plus some excited states with energies between 2075 and 3550 cm−1. These data have been fitted to an effective Hamiltonian which takes into account rotational and vibrational l-type resonance effects, together with a number of anharmonic interaction terms. On average, all the analysed data are reproduced within the experimental accuracy. About 90 000 rotational and ro-vibrational transition frequencies have been computed on the basis of the spectroscopic constants obtained from the global fit in order to support data interpretation and astronomical searches in the interstellar medium and planetary atmospheres. Part of these data is included in the 2020 release of the HITRAN database.

Published high-resolution rotation-vibration transitions of H212C16O, the principal isotopologue of methanal, are analyzed using the MARVEL (Measured Active Rotation-Vibration Energy Levels) procedure. The literature results are augmented by new, high-accuracy measurements of pure rotational transitions within the ground, ν3, ν4, and ν6 vibrational states. Of the 16 596 non-redundant transitions processed, which come from 43 sources including the present work, 16 403 could be validated, providing 5029 empirical energy levels of H212C16O with statistically well-defined uncertainties. All the empirical rotational-vibrational energy levels determined are used to improve the accuracy of ExoMol's AYTY line list for hot formaldehyde. The complete list of collated experimental transitions, the empirical energy levels determined, as well as the extended and improved line list are provided as Supplementary Material.

Observations of ammonia in interstellar environments have revealed high levels of deuteration, and all its D-containing variants, including ND$_3$, have been detected in cold prestellar cores and around young protostars. The observation of these deuterated isotopologues is very useful to elucidate the chemical and physical processes taking place during the very early stages of star formation, as the abundance of deuterated molecules is highly enhanced in dense and cold gas. Nitrogen hydride radicals are key species lying at the very beginning of the reaction pathway leading to the formation of NH$_3$ and organic molecules of pre-biotic interest, but relatively little information is known about their D-bearing isotopologues. To date, only ND has been detected in the interstellar gas. To aid the identification of further deuterated nitrogen radicals, we have thoroughly re-investigated the rotational spectrum of NHD employing two different instruments: a frequency-modulation submillimetre spectrometer operating in the THz region and a synchrotron-based Fourier Transform infrared spectrometer operating in the 50-240 cm$^{-1}$ wavelength range. NHD was produced in a plasma of NH$_3$ and D$_2$. A wide range of rotational energy levels has been probed thanks to the observation of high $N$ (up to 15) and high $K_a$ (up to 9) transitions. A global analysis including our new data and those already available in the literature has provided a comprehensive set of very accurate spectroscopic parameters. A highly reliable line catalogue has been generated to assist archival data searches and future astronomical observations of NHD at submillimetre and THz regimes., 16 pages, 3 figures

Trideuterated 1-phosphapropyne (CD3CP) has been produced by co-pyrolysis of phosphorus trichloride and esadeuterated ethane. The rotational spectra of CD3CP in the ground and the low-lying vibrational states v8 (CCP bending mode) and 2 v8 have been investigated in the millimeter-wave region. Very accurate values of the quartic centrifugal distortion constants DJ and DJK and of the sextic distortion constants HJK and HKJ have been obtained for the ground state. l-type resonance effects have been taken into account in the analysis of the spectra of the degenerate bending states, so that the energy difference between the v8|l| = 20, and v8|l| = 22 states could be determined, together with a number of spectroscopic constants involved in the l-type resonance. Moreover, for the parent isotopologue CH3CP a new set of excited-state lines (v8 = 1, 2 and v4 = 1) were recorded up to 330 GHz, and a global analysis including all available rotational and rovibrational transitions related to the ground and v8 = 1, 2 states has been performed. A satisfactory fit could only be obtained by making a reassignment of the few transition wavenumbers previously measured for the 2ν80 ← ν8±1 hot band [M.K. Bane et al., J. Mol. Spectrosc. 275 (2012) 9–14]. The experimental work has been combined with quantum-chemical computations. Quadratic and cubic force constants of 1-phosphapropyne have been calculated at MP2 level of theory with a basis set of triple-ζ quality. A semi-experimental equilibrium structure has been derived by correcting experimental ground-state rotational constants by means of theoretical vibration-rotation interaction constants.

Huge efforts have recently been taken in the derivation of accurate compilations of rovibrational energies of water, one of the most important reference systems in spectroscopy. Such precision is desirable for all water isotopologues, although their investigation is challenged by hyperfine effects in their spectra. Frequency-comb locked noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy (NICE-OHMS) allows for achieving high sensitivity, resolution, and accuracy. This technique has been employed to resolve the subtle hyperfine splittings of rovibrational transitions of H$_{2}$$^{17}$Oin the near-infrared region. Simulation and interpretation of the H$_{2}$$^{17}$Osaturation spectra have been supported by coupled-cluster calculations performed with large basis sets and accounting for high-level corrections. Experimental $^{17}$O hyperfine parameters are found in excellent agreement with the corresponding computed values. The need of including small hyperfine effects in the analysis of H$_{2}$$^{17}$O spectra has been demonstrated together with the ability of the computational strategy employed for providing quantitative predictions of the corresponding parameters.

The pure rotational spectra of the amidogen radical 15ND2 and of the imidogen radicals 15ND and 15NH were recorded by a millimetre- and a submillimetre-wave spectrometer up to the THz region. This work represents the first experimental laboratory detection of both 15ND2 and 15ND. In the case of the amidogen radical, the analysis of the data provided a large set of rotational, electron spin-rotation and hyperfine terms. In the case of 15ND, our transitions were merged with the already existing data for NH, ND and 15NH and analysed in a multi-isotopologue Dunham-type fit. As far as 15NH is concerned, the N = 1-0 transition, for which just one fine-structure component was known (Bailleux S, Martin-Drumel MA, Margulés L, Pirali O, Wlodarczak G, Roy P, Roueff E, Gerin M, Faure A, Hily-Blant P. High-resolution Terahertz spectroscopy of the 15NH 3S-. Astron Astrophys 2012; 538: A135(1--5)), was detected around 1 THz..

Phosphorous-containing molecules have a great relevance in prebiotic chemistry in view of the fact that phosphorous is a fundamental constituent of biomolecules, such as RNA, DNA, and ATP. Its biogenic importance has led astrochemists to investigate the possibility that P-bearing species could have formed in the interstellar medium (ISM) and subsequently been delivered to early Earth by rocky bodies. However, only two P-bearing molecules have been detected so far in the ISM, with the chemistry of interstellar phosphorous remaining poorly understood. Here, in order to shed further light on P-carriers in space, we report a theoretical spectroscopic characterisation of the rotational spectrum of POH in its 3A″ ground electronic state. State-of-the-art coupled-cluster schemes have been employed to derive rotational constants, centrifugal distortion terms, and most of the fine and hyperfine interaction parameters, while the electron spin–spin dipolar coupling has been investigated using the multi-configuration self-consistent-field method. The computed spectroscopic parameters have been used to simulate the appearance of triplet POH rotational and ro-vibrational spectra in different conditions, from cold to warm environments, either in gas-phase experiments or in molecular clouds. Finally, we point out that the predicted hyperfine structures represent a key pattern for the recognition of POH in laboratory and interstellar spectra.

The cyanate anion (NCO-) is a species of considerable astrophysical relevance. It is widely believed to be embedded in interstellar ices present in young stellar objects but has not yet been detected in the dense gas of the interstellar medium. Here we report highly accurate laboratory measurements of the rotational spectrum of the N13CO-isotopologue at submillimeter wavelengths along with the detection of three additional lines of the parent isotopologue up to 437.4 GHz. With this new data, the rotational spectrum of both isotopologues can be predicted to better 0.25 km s-1in equivalent radial velocity up to 1 THz, more than adequate for an astronomical search in any source. Moreover, a semiexperimental equilibrium structure of the anion is derived by combining the experimental ground-state rotational constants of the two isotopologues with theoretical vibrational corrections, obtained by using the coupled-cluster method with inclusion of single and double excitations and perturbative inclusion of triple excitations (CCSD(T)). The estimated accuracy of the two bond distances is on the order of 5 × 10-4Å: a comparison to the values obtained by geometry optimization with the CCSD(T) method and the use of a composite scheme, including additivity and basis-set extrapolation techniques, reveals that this theoretical procedure is very accurate.

International audience; Prebiotic sugars are thought to be formed on primitive Earth by the formose reaction. However, their formation is not fully understood and it is plausible that key intermediates could have formed in extraterrestrial environments and subsequently delivered on early Earth by cometary bodies. 1,2-Ethenediol, the enol form of glycolaldehyde, represents a highly reactive intermediate of the formose reaction and is likely detectable in the interstellar medium. Here, we report the identification and first characterization of (Z)-1,2-ethenediol by means of rotational spectroscopy. The title compound has been produced in the gas phase by flash vacuum pyrolysis of bis-exo-5-norbornene-2,3-diol at 750 degrees C, through a retro-Diels-Alder reaction. The spectral analysis was guided by high-level quantum-chemical calculations, which predicted spectroscopic parameters in very good agreement with the experiment. Our study provides accurate spectral data to be used for searches of (Z)-1,2-ethenediol in the interstellar space.

Nitriles play a key role as molecular precursors in prebiotic experiments based on the RNA-world scenario for the origin of life. These chemical compounds could have been partially delivered to the young Earth from extraterrestrial objects, stressing the importance of establishing the reservoir of nitriles in the interstellar medium. We report here the detection towards the molecular cloud G+0.693-0.027 of several nitriles, including cyanic acid (HOCN), and three C$_4$H$_3$N isomers (cyanoallene, CH$_2$CCHCN; propargyl cyanide, HCCCH$_2$CN; and cyanopropyne (CH$_3$CCCN), and the tentative detections of cyanoformaldehyde (HCOCN), and glycolonitrile (HOCH$_2$CN). We have also performed the first interstellar search of cyanoacetaldehyde (HCOCH$_2$CN), which was not detected. Based on the derived molecular abundances of the different nitriles in G+0.693-0.027 and other interstellar sources, we have discussed their formation mechanisms in the ISM. We propose that the observed HOCN abundance in G+0.693-0.027 is mainly due to surface chemistry and subsequent shock-induced desorption, while HCOCN might be mainly formed through gas-phase chemistry. In the case of HOCH$_2$CN, several grain-surface routes from abundant precursors could produce it. The derived abundances of the three C$_4$H$_3$N isomers in G+0.693-0.027 are very similar, and also similar to those previously reported in the dark cold cloud TMC-1. This suggests that the three isomers are likely formed through gas-phase chemistry from common precursors, possibly unsaturated hydrocarbons (CH$_3$CCH and CH$_2$CCH$_2$) that react with the cyanide radical (CN). The rich nitrile feedstock found towards G+0.693-0.027 confirms that interstellar chemistry is able to synthesize in space molecular species that could drive the prebiotic chemistry of the RNA-world., Comment: Accepted in Frontiers in Astronomy and Space Sciences

Huge efforts have recently been taken in the derivation of accurate compilations of rovibrational energies of water, one of the most important reference systems in spectroscopy. Such precision is desirable for all water isotopologues, although their investigation is challenged by hyperfine effects in their spectra. Frequency-comb locked noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy (NICE-OHMS) allows for achieving high sensitivity, resolution, and accuracy. This technique has been employed to resolve the subtle hyperfine splittings of rovibrational transitions of H217O in the near-infrared region. Simulation and interpretation of the H217O saturation spectra have been supported by coupled-cluster calculations performed with large basis sets and accounting for high-level corrections. Experimental17O hyperfine parameters are found in excellent agreement with the corresponding computed values. The need of including small hyperfine effects in the analysis of H217O spectra has been demonstrated together with the ability of the computational strategy employed for providing quantitative predictions of the corresponding parameters.

The escalating identification of new complex molecules in the interstellar medium claims for potential formation routes of such species. In this regard, the present work considers the reaction between oxirane and the CN radical as a feasible formation mechanism of species having the C3H3NO molecular formula. Indeed, the compounds of this family are elusive in the interstellar medium and suggestions on which species could be formed at low temperature and low pressure conditions might aid their discovery. The c-C2H4O + CN reaction has been investigated from the thermodynamic and kinetic points of view. The thermodynamic has been studied by means of a double-hybrid density functional and revealed the presence of several mechanisms submerged with respect to the reactants energy, with the potential formation of oxazole and cyanoacetaldehyde. However, the kinetic results suggest that the main reaction pathway is the H-extraction, leading to 2-oxiranyl radical and HCN. The formation of cyanoacetaldehyde + H and of H2CCN + H2CO is also possible with smaller rate constants, while the production of oxazole is negligible due to the presence of a high energy barrier.

The conformational isomerism of isopropylamine and n-propylamine has been investigated by means of an integrated strategy combining high-level quantum-chemical calculations and high-resolution rotational spectroscopy. The equilibrium structures (and thus equilibrium rotational constants) as well as relative energies of all conformers have been computed using the so-called "cheap" composite scheme, which combines the coupled-cluster methodology with second-order Møller-Plesset perturbation theory for extrapolation to the complete basis set. Methods rooted in the density functional theory have been instead employed for computing spectroscopic parameters and for accounting for vibrational effects. Guided by quantum-chemical predictions, the rotational spectra of isopropylamine and n-propylamine have been investigated between 2 and 400 GHz with Fourier transform microwave and frequency-modulation millimeter/submillimeter spectrometers. Spectral assignments confirmed the presence of several conformers with comparable stability and pointed out possible Coriolis resonance effects between some of them.

Cyclopropanecarboxaldehyde (CPCA) has two main conformers, syn and anti, that are renowned for being very close in energy. Thestability order of these two main species is constantly reversed by changing the level of theory or the experimental technique employed in its determination. The anti conformer is predicted to be the most favoured in condensed states of matter, but uncertainty still remains on the relative stability in the gas phase. To gain further insights into this issue, the investigation of the rotational spectrum of both syn- and anti-CPCA has been extended in the 246–294 GHz frequency region and complemented by a detailed computational study of both conformers. A fit incorporating the recorded rotational transitions as well as those reported in the literature led to the accurate determination of the rotational parameters, also including high-order centrifugal distortion constants. Accurately computed vibrational frequencies were used to re-analyse the infrared spectrum of both conformers, thereby allowing a re-assignment of two vibrational bands, namely (Formula presented.) of anti-CPCA and (Formula presented.) of the syn conformer. While our state-of-the-art computations favour the anti conformer in the stability order, estimates from analysis of rotational spectra are rather controversial and are strongly affected by several factors, such as the zero-point vibrational correction.

In light of its ubiquitous presence in the interstellar gas, the chemistry and reactivity of the HCO+ ion requires special attention. The availability of up-to-date collisional data between this ion and the most abundant perturbing species in the interstellar medium is a critical resource in order to derive reliable values of its molecular abundance from astronomical observations. This work intends to provide improved scattering parameters for the HCO+ and He collisional system. We have tested the accuracy of explicitly correlated coupled-cluster methods for mapping the short- and long-range multi-dimensional potential energy surface of atom-ion systems. A validation of the methodology employed for the calculation of the potential well has been obtained from the comparison with experimentally derived bound-state spectroscopic parameters. Finally, by solving the close-coupling scattering equations, we have derived the pressure broadening and shift coefficients for the first six rotational transitions of HCO+ as well as inelastic state-to-state transition rates up to j = 5 in the 5-100 K temperature interval., 8 pages, 5 figures

The first high-resolution infrared spectra of CH2D37Cl have been investigated in the region 650–1100 cm−1 where the lowest fundamental bands ν5 (826.2626 cm−1), ν6 (708.4307 cm−1), and ν9 (986.3405 cm−1) occur. These vibrations perturb each other by different weak interactions and the v5 = 1 and v6 = 1 states were treated according to a model which accounts for a c-type Coriolis resonance. The spectral analysis resulted in the identification of 1664, 2550 and 2657 ro-vibrational transitions for ν5, ν6, and ν9 bands respectively, and to the determination of accurate spectroscopic parameters by using the Watson’s A-reduction Hamiltonian in the Ir representation. The simulations of the ro-vibrational structure of the ν5, ν6, and ν9 bands performed in different spectral regions adequately reproduce the experimental data.

Cyanoacetylene, the simplest cyanopolyyne, is an abundant interstellar molecule commonly observed in a vast variety of astronomical sources. Despite its importance as a potential tracer of the evolution of star-forming processes, the deuterated form of cyanoacetylene is less observed and less studied in the laboratory than the main isotopologue. Here, we report the most extensive spectroscopic characterization of DC$_3$N to date, from the millimeter domain to the infrared region. Rotational and ro-vibrational spectra have been recorded using millimeter-wave frequency-modulation and Fourier-transform infrared spectrometers, respectively. All the vibrational states with energy up to 1015 cm$^{-1}$ have been analyzed in a combined fit, where the effects due to anharmonic resonances have been adequately accounted for. The analysis contains over 6500 distinct transition frequencies, from which all the vibrational energies have been determined with good precision for many fundamental, overtone, and combination states. This work provides a comprehensive line catalog for astronomical observations of DC$_3$N, 14 pages, 3 figures, 8 tables, accepted for publication in JQSRT

Aminoacetonitrile, a molecule detected in the interstellar medium only towards the star-forming region Sagittarius B2 (Sgr B2) thus far, is considered an important prebiotic species. To date, observations were limited to ground state emission lines, whereas transitions from within vibrationally excited states remained undetected. We wanted to accurately determine the energies of the low-lying vibrational states of aminoacetonitrile, which are expected to be populated in Sgr B2(N1), the main hot core of Sgr B2(N). This step is fundamental in order to properly evaluate the vibration-rotation partition function of aminoacetonitrile as well as the line strengths of the rotational transitions of its vibrationally excited states. This is necessary to derive accurate column densities and secure the identification of these transitions in astronomical spectra. The far-infrared ro-vibrational spectrum of aminoacetonitrile has been recorded in absorption against a synchrotron source of continuum emission. Three bands, corresponding to the lowest vibrational modes of aminoacetonitrile, were observed in the frequency region below 500 cm$^{-1}$. The combined analysis of ro-vibrational and pure rotational data allowed us to prepare new spectral line catalogs for all the states under investigation. We used the imaging spectral line survey ReMoCA performed with ALMA to search for vibrationally excited aminoacetonitrile toward Sgr B2(N1). On the basis of these spectroscopic predictions, we report the interstellar detection of aminoacetonitrile in its $v_{11}=1$ and $v_{18}=1$ vibrational states toward Sgr B2(N1) in addition to emission in its vibrational ground state. The intensities of the identified $v_{11}=1$ and $v_{18}=1$ lines are consistent with the detected $v=0$ lines under LTE at a temperature of 200 K for an aminoacetonitrile column density of $1.1 \times 10^{17}$ cm$^{-2}$., 14 pages, 7 figures, 5 tables, accepted for publication in A&A

In the present work we carried out a combined rotational and ro-vibrational investigation on 1,1,2-trifluoroethene, a relevant unsaturated hydrofluoroolefin recently proposed as refrigerant in mixture with other halogenated compounds (like difluoromethane). By employing a frequency-modulation millimeter-wave spectrometer, the rotational spectra were recorded in the frequency ranges 80–96 GHz and 245–260 GHz for the ground and also the vibrationally excited states ν 8 = 1 , ν 9 = 1 , ν 12 = 1 , ν 9 = 2 , ν 12 = 2 , and ν 9 = ν 12 = 1 . In addition, the infrared spectra in the region of the ν6 band (centered at 929.8 cm − 1 ) were measured with a high-resolution Fourier transform spectrometer. The data coming from the detailed rotational and ro-vibrational assignments were combined in a global fit, taking into account also the ground state transitions available in the literature. From this analysis, a very accurate set of rotational and centrifugal distortion constants was determined for the ground state and for all the vibrationally excited states here investigated.