Context. The hydroxymethyl radical (CH2OH) is one of two structural isomers, together with the methoxy radical (CH3O), that can be produced by abstraction of a hydrogen atom from methanol (CH3OH). In the interstellar medium (ISM), both CH2OH and CH3O are suspected to be intermediate species in many chemical reactions, including those of formation and destruction of methanol. The determination of the CH3O/CH2OH ratio in the ISM would bring important information concerning the formation processes of these species in the gas and solid phases. Interestingly, only CH3O has been detected in the ISM so far, despite the recent first laboratory measurement of the CH2OH rotation-tunneling spectrum. This lack of detection is possibly due to the non-observation in the laboratory of the most intense rotation-tunneling transitions at low temperatures. Aims. To support further searches for the hydroxymethyl radical in space, we present a thorough spectroscopic study of its rotation-tunneling spectrum, with a particular focus on transitions involving the lowest quantum numbers of the species. Methods. We recorded the rotation-tunneling spectrum of CH2OH at room temperature in the millimeter-wave domain using a frequency multiplication chain spectrometer. A fluorine-induced H-abstraction method from methanol was used to produce the radical. Results. About 180 transitions were observed, including those involving the lowest N and Ka quantum numbers, which are predicted to be intense under cold astrophysical conditions. These transitions were fitted together with available millimeter-wave lines from the literature. A systematic observation of all components of the rotational transitions yields a large improvement of the spectroscopic parameters allowing confident searches of the hydroxymethyl radical in cold to warm environments of the ISM.

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We present a thorough pure rotational investigation of the CH 2 CN radical in its ground vibrational state. Our measurements cover the millimeter and sub-millimeter wave spectral regions (79−860 GHz) using a W-band chirped-pulse instrument and a frequency multiplication chain-based spectrometer. The radical was produced in a flow cell at room temperature by H abstraction from acetonitrile using atomic fluorine. The newly recorded transitions of CH 2 CN (involving N″ and K a ″ up to 42 and 8, respectively) were combined with the literature data, leading to a refinement of the spectroscopic parameters of the species using a Watson S-reduced Hamiltonian. In particular, the A rotational constant and K-dependent parameters are significantly better determined than in previous studies. The present model, which reproduces all experimental transitions to their experimental accuracy, allows for confident searches for the radical in cold to warm environments of the interstellar medium.

Context. The recent interstellar detections of -CN containing aromatic species, namely benzonitrile, 1-cyanonaphthalene, and 2cyanonaphthalene, bring renewed interest in related molecules that could participate in similar reaction networks. Aims. To enable new interstellar searches for benzonitrile derivatives, the pure rotational spectra of several related species need to be investigated in the laboratory. Methods. We have recorded the pure rotational spectra of ortho-and meta-dicyanobenzene in the centimetre and millimetre-wave domains. Assignments were supported by high-level quantum chemical calculations. Using Markov chain Monte Carlo simulations, we also searched for evidence of these molecules towards TMC-1 using the GOTHAM survey. Results. Accurate spectroscopic parameters are derived from the analysis of the experimental spectra, allowing for reliable predictions at temperatures of interest (i.e. 10-300 K) for astronomical searches. Our searches in TMC-1 for both ortho-and meta-isomers provide upper limits for the abundances of the species.

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The (sub-)millimeter wave spectrum of the non-rigid CH2OH radical is investigated both experimentally and theoretically. Ab initio calculations are carried out to quantitatively characterize its potential energy surface as a function of the two large amplitude ∠H1COH and ∠H2COH dihedral angles. It is shown that the radical displays a large amplitude torsional-like motion of its CH2 group with respect to the OH group. The rotation–torsion levels computed with the help of a 4D Hamiltonian accounting for this torsional-like motion and for the overall rotation exhibit a tunneling splitting, in agreement with recent experimental investigations, and a strong rotational dependence of this tunneling splitting on the rotational quantum number K a due to the rotation–torsion Coriolis coupling. Based on an internal axis method approach, a fitting Hamiltonian accounting for tunneling effects and for the fine and hyperfine structure is built and applied to the fitting of the new (sub)-millimeter wave transitions measured in this work along with previously available high-resolution data. 778 frequencies and wavenumbers are reproduced with a unitless standard deviation of 0.79 using 27 parameters. The N = 0 tunneling splitting, which could not be determined unambiguously in the previous high-resolution investigations, is determined based on its rotational dependence.

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A decade ago, the advent of broadband chirped-pulse Fourier-transform microwave spectrometers revolutionized rotational spectroscopy in the centimeter-wave region [1]. Commercial solution are available in the millimeter-wave region, and new molecular spectroscopy investigations can now be undertaken.Motivated by the prospect of enabling new interstellar detections, we have developed a new set-up associating a broadband chirped-pulse Fourier-transform millimeter-wave (W-band) spectrometer and a supersonic jet chamber. Radicals are produced by an electric discharge in the high pressure part of the jet and reactive species are directly probed by the radiation at temperatures as low as few Kelvin.Using different organic precursors such as acetonitrile (CH 3 CN), methanol (CH 3 OH) or allene (C 3 H 4 ), we were able to study rich discharge mixtures. Among others, we were able to produce and detect the cyanomethyl radical (CH 2 CN)[2], the methoxy radical (CH 3 O) [3] and cyclopropenylidene (c − C 3 H 2 ) [4] in the vibrational ground state and in several vibrational excited states. In the presentation, technical details of the set-up will be provided, together with the preliminary results we obtained.