Search

We report the detection of methyl ketene towards TMC-1 with the QUIJOTE line survey. Nineteen rotational transitions with rotational quantum numbers ranging from J = 3 up to J = 5 and Ka ≤ 2 were identified in the frequency range 32.0–50.4 GHz, 11 of which arise above the 3σ level. We derived a column density for CH3CHCO of N = 1.5 × 1011 cm−2 and a rotational temperature of 9 K. Hence, the abundance ratio between ketene and methyl ketene, CH2CO/CH3CHCO, is 93. This species is the second C3H4O isomer detected. The other, trans-propenal (CH2CHCHO), corresponds to the most stable isomer and has a column density of N = (2.2 ± 0.3)×1011 cm−2, which results in an abundance ratio CH2CHCHO/CH3CHCO of 1.5. The next non-detected isomer with the lowest energy is cis-propenal, which is therefore a good candidate for future discovery. We have carried out an in-depth study of the possible gas-phase chemical reactions involving methyl ketene to explain the abundance detected, achieving good agreement between chemical models and observations.

The interstellar detections of isocyanic acid, methyl isocyanate, and very recently also ethyl isocyanate, open the question of the possible detection of vinyl isocyanate in the interstellar medium. The aim of this study is to extend the laboratory rotational spectrum of vinyl isocyanate into the millimeter wave region and to undertake a check for its presence in the high-mass star forming region Sgr B2. The rotational spectrum of vinyl isocyanate was recorded in the frequency regions 127.5-218 and 285-330 GHz using the Prague millimeter wave spectrometer. The spectral analysis was supported by high-level quantum-chemical calculations. We assumed local thermodynamic equilibrium to compute synthetic spectra of vinyl isocyanate and to search for it in the ReMoCA survey performed with ALMA toward Sgr B2(N). We also searched for ethyl isocyanate in the same source. Accurate values for the rotational and centrifugal distortion constants are reported for the ground vibrational states of trans and cis vinyl isocyanate. We report nondetections of vinyl and ethyl isocyanate toward the main hot core of Sgr B2(N). We find that vinyl and ethyl isocyanate are at least 11 and 3 times less abundant than methyl isocyanate in this source, respectively. Although the precise formation mechanism of interstellar methyl isocyanate itself remains uncertain, we infer from existing astrochemical models that our observational upper limit for the CH3NCO:C2H5NCO ratio in Sgr B2(N) is consistent with ethyl isocyanate being formed on dust grains via the abstraction or photodissociation of an H atom from methyl isocyanate, followed by the addition of a methyl radical. The dominance of such a process for ethyl isocyanate production, combined with the absence of an analogous mechanism for vinyl isocyanate, would indicate that the ratio C2H3NCO:C2H5NCO should be rather less than unity., Comment: Accepted for publication in A&A

The rotational spectrum (4-40 GHz and 50-330 GHz) has been measured and analyzed for trifluoroacetaldehyde, also known as fluoral (CF

Aims. The recent detection of cyanomethanimine in the interstellar medium makes its methyl derivative, 2-iminopropanenitrile (CH3C(CN)NH), a promising candidate for an interstellar detection. The aim of this work is to extend the current knowledge of the laboratory rotational spectrum to higher frequencies, which is an essential prerequisite for an identification of the molecular species in the interstellar medium by millimetre-wave astronomy. Methods. The room-temperature rotational spectrum of 2-iminopropanenitrile has been measured in several frequency regions between 128 and 329 GHz. The A–E splittings of the rotational transitions arising from the methyl top internal rotation were analysed employing the ERHAM and XIAM programs. Results. A dataset of approximately 900 newly assigned rotational transitions in the ground state of the Z isomer and a set of refined molecular constants, including the internal rotation parameters, are reported. Moreover, this work provides the first spectral characterisation of the less stable E isomer ground state, as well as the three lowest-lying vibrationally excited states of the Z isomer, v21 = 1, v14 = 1, and v20 = 1. This comprehensive spectroscopic study will allow a search for 2-iminopropanenitrile in the millimetre-wave surveys of interstellar sources, such as those recorded by the Atacama Large Millimeter/submillimeter Array.

Methyl isocyanate (CH3NCO) was recently found in hot cores and suggested on comet 67P/CG. The incorporation of this molecule into astrochemical networks requires data on its formation and destruction. In this work, ices of pure CH3NCO and of CH3NCO(4-5%)/H2O mixtures deposited at 20 K were irradiated with a UV D2 lamp (120-400 nm) and bombarded by 5 keV electrons to mimic the secondary electrons produced by cosmic rays (CRs). The destruction of CH3NCO was studied using IR spectroscopy. After processing, the νa-NCO band of CH3NCO disappeared and IR bands corresponding to CO, CO2, OCN- and HCN/CN- appeared instead. The products of photon and electron processing were very similar. Destruction cross sections and half-life doses were derived from the measurements. Water ice provides a good shield against UV irradiation (half-life dose of ~ 64 eV molecule-1 for CH3NCO in water-ice), but not so good against high-energy electrons (half-life dose ~ 18 eV molecule-1). It was also found that CH3NCO does not react with H2O over the 20-200 K temperature range. These results indicate that hypothetical CH3NCO in the ices of dense clouds should be stable against UV photons and relatively stable against CRs over the lifetime of a cloud (~ 107 yr), and could sublime in the hot core phase. On the surface of a Kuiper belt object (the original location of comet 67P/CG) the molecule would be swiftly destroyed, both by photons and CRs, but embedded below just 10 μm of water-ice, the molecule could survive for ~ 109 yr.

The gas-phase basicities of the title compounds have been determined by Fourier transform ion cyclotron resonance mass spectrometry. Arsines are systematically weaker bases than phosphines. Basicity decreases in both series in the order ethyl > ethenyl > ethynyl. On the basis of their ionization energies, the phosphorus atom is recognized as the preferred site of protonation in the phosphines studied. A similar reasoning applied to arsines does not allow a clear-cut conclusion to be made. As it appears from the experimental results of this study and the few data on alkyl and phenyl derivatives available in the literature, substituent effects are attenuated by a factor of approximately 1.15 when going from phosphines to arsines.

What is the role played by amino acids in the chemistry of the interstellar medium and the emergence of life on the early Earth? Are they really the primary key compounds as free amino acids? Is their presence or absence in the interstellar medium a significant problem? How to get an amino acid sample with an enantiomeric excess on the early Earth or ISM? How to increase the enantiomeric excess to have pure enantiomers? All these questions have received partial answers but they remain open and probably they will still be open for several more decades.

α,α′-dichlorophophines, easily obtained by chemoselective reduction of the corresponding phosphonates, can be considered as precursors of unhindered C-chlorophosphaethylenes and synthetic equivalents of phospha-acetylenes.

In the title compound, {2-[(dimethylamino-κN)-methyl]phenyl-κC}(4-diphenylphosphino-κP-3-methyl-1-phenyl-5-pyrazololato-κO)palladium(II) 0.5-benzene solvate, [Pd(C 22 H 18 N 2 OP)(C 9 H 12 N)].0.5C 6 H 6 , the Pd atom, which is in a quasi-planar environment, is complexed by two chelating three-electron-donor ligands, with P and N atoms occupying trans positions. The plane defined by the aromatic pyrazole ring is coplanar with the metal plane. The angle between the N-bonded phenyl ring and the metal plane is 8 o

International audience; About 160 molecules have been detected in the interstellar medium, the comae and the atmospheres of planets. The presence of these compounds leads to imagine a chemistry of these media to explain the formation of these species and to predict the possible presence of other ones. Many of them have never been synthesized or isolated in labs and their preparation can be challenging, up to necessitate news reactions or special equipments.

α,α′-dichlorophophines, easily obtained by chemoselective reduction of the corresponding phosphonates, can be considered as precursors of unhindered C-chlorophosphaethylenes and synthetic equivalents of phospha-acetylenes.

α-Dichlorophosphine (3), easily obtained by chemoselective phosphonate reduction, is a precursor of the unhindered C-chlorophosphaethylene (4) and a synthetic equivalent of the phospha-acetylene (5).

Reactive methyleneamines bearing alkyl or functional groups are isolated at low temperature in the condensate state by flash vacuum thermolysis of α-aminonitriles and subsequent vapour phase HCN removal on solid base.