Search

A Fourier-transform microwave spectrum of the cis-β-cyanovinyl radical is re-measured for the Ka = 0 ladder of the a-type transitions up to 30 GHz and the 212–111 transition at 19.85 GHz.

7 pags., 4 figs., 3 tabs., Fourier transform microwave spectra for two isomers of the chlorine substituted vinyl radical have been observed in the 4-52 GHz frequency region. The observed radicals (2A') have been generated using electric discharges of diluted dichloro derivatives of ethylene as molecular precursors. Fine and hyperfine components observed for each rotational transition are fully assigned in the present study to two isotopologues (35Cl and 37Cl), and precise molecular constants are determined for both radicals., The present study was supported by the Ministry of Science and Technology of Taiwan, MOST 104-2113-M-009-202. JCG thanks the Centre National d’Etudes Spatiales (CNES) for a grant.

The HOSO2 radical was detected by microwave spectroscopy in a discharge plasma of a SO2/H2O gas mixture. The observed spectrum shows tunneling splittings due to the OH torsional motion. A least-squares analysis considering interactions between the two torsional sublevels of the ground vibronic state, 0+ and 0−, reproduces the observed transition frequencies with a standard deviation of ca. 3 kHz. The splitting between the two torsional sublevels is accurately determined to be 24.3 MHz for HOSO2 and 0.08 MHz for DOSO2. The potential barrier for the OH torsional motion is estimated to be 1150 cm−1 from a one-dimensional hindered rotor model.

Pure rotational transitions of methyl vinyl ketone oxide, or the so called methyl-vinyl Criegee intermediate, were observed by Fourier-transform microwave spectroscopy. Among the four possible conformers of this species, predicted by theory within an energy window of 3 kcal/mol, only the lowest-energy conformer, the syn-trans form, was detected in a discharged jet of a 1,3-diiode-but-2-ene (either in Z- or E-conformation) and O2 mixture diluted in Ar. Thirty pure rotational transitions with internal rotation splitting of the methyl top were observed. The observed frequencies were analyzed by the XIAM program, yielding an internal rotation barrier of 702.8(28) cm-1, which reasonably agrees with a theoretical value of 680 cm-1 determined with CCSD(T)/cc-pVTZ.

34 pags., 15 figs., 3 tabs., Carbonyl oxides, RRCOO, alternatively known as Criegee intermediates (CIs), are short-lived molecules produced from ozonolysis of alkenes. These ozonolysis reactions yield highly excited CIs, and most of them promptly decay with emission of the OH radical and other products. Some of the nascent CIs are stabilised by collisional relaxation with surrounding molecules, and react with atmospheric trace constituents, such as SO and gaseous organic compounds, converting them to more highly oxygenated molecules relevant to formation of aerosols. Hence, reactions of CIs are of central interest for atmospheric chemists. Physico-chemical properties of CIs are strongly related to their geometrical and electronic structures, which are often discussed based on spectroscopic information. Especially, very high resolution rotational spectroscopy provides critical information about molecular structures and intramolecular dynamics, and also enables us to probe individual isomers, conformers, and isotopologues, with complete selectivity. This article reviews the rotational investigations carried out on several CIs, their bimolecular complexes and primary reaction products, focusing on their molecular structure, conformational behaviour and reactivity., This research was supported by JSPS KAKENHI Grant Nos. 19205002 (Y.E.), 25410004 (M.N. and Y.E.) and 15K05378 (M.N.) and by the Ministry of Science and Technology of Taiwan under Grant Nos. MOST 104-2113-M-009-020 (Y.E.) and MOST 105-2811-M-009-026 and 106-2811-M-009- 023 (C.C.).

10 pags., 4 figs., 2 tabs., Rapid reactions of carboxylic acids with Criegee intermediates provide efficient gas phase removal processes and are proposed to trigger the formation of new molecular compounds, which are implicated in the growth of atmospheric aerosols. The new adducts formed in these reactions are known as hydroperoxide esters and are predicted to be condensable, with lower vapor pressures than the reactants. We report here the direct detection of hydroperoxyethyl formate (HOOCH(CH3)OCHO) formed in the gas phase reaction between the methyl substituted Criegee intermediate, CH3CHOO, and formic acid. Two different isomers of this hydroperoxide ester have been observed using the combination of pulsed Fourier-transform microwave spectroscopy with isotopic substitution experiments and high-level quantum chemical calculations. The identification of hydroperoxyethyl formate as the main nascent product of the CH3CHOO and HCOOH reaction differs from previous results that reported the formation of vinyl hydroperoxide as the reaction product of this reaction., This research was supported by the Ministry of Science and Technology of Taiwan under Grant Nos MOST 104-2113-M-009-020 (Y. E.) and MOST 105-2811-M-009-026 and 106-2811-M-009- 023 (C. C.).

The 101–000 and 202–101 rotational transitions of a monohalomethylene, HCI, are observed in a discharge plasma of diiodomethane by Fourier-transform microwave (FTMW) and FTMW-microwave double-resonance spectroscopy. The effective rotational constant ( B + C ) / 2 , the centrifugal distortion constant Δ J , and the quadrupole coupling constant of the iodine nucleus are determined from the observed line frequencies. The nuclear spin-rotation coupling constant C bb is required to be included into the set of fitting parameters for a satisfactory analysis of the observed line frequencies.

Pure rotational transitions of cis-OSOO are identified in a discharge plasma of a SO2 and O2 gaseous mixture by Fourier-transform microwave (FTMW) and FTMW-MW double-resonance spectroscopy. Both a- and b-type transitions are observed for this molecule, and the rotational and centrifugal distortion constants are precisely determined from the observed line positions. The inertial defect calculated from the determined rotational constants indicates that the cis-OSOO molecule has a planar equilibrium geometry in the ground vibronic state.

The microwave spectrum of the doubly deuterated cyanomethyl radical (D2CCN) in its ground electronic state ((2) B (1)) has been observed for the lowest four rotational transitions (N(Ka,Kc) = 1(0,1)–0(0,0), 2(0,2)–1(0,1), 2(1,2)–1(0,1) and 2(1,1)–1(1,0)) using a Fourier transform microwave spectrometer in combination with a pulsed discharge nozzle. A total of 394 hyperfine components were measured and subjected to a least squares analysis which allowed determining twelve hyperfine constants for nitrogen and deuterium nuclei. With this new set of molecular constants we obtained accurate predictions for low N rotational transitions with hyperfine structure, and searched for this species in TMC–1.

6 pags., 3 figs., 3 tabs., The reaction system between the simplest Criegee intermediate, CHOO, and the greenhouse gas CO has been investigated by Fourier transform microwave spectroscopy. The CHOO-CO weakly bound complex was identified in the rotational spectrum, where inversion doublets due to the tunnelling motion between two equivalent configurations of the complex, with CO located at one side or the other side of the CHOO plane, were observed. Using a two-state torsion-rotation Hamiltonian, a complete set of rotational and centrifugal distortion constants for both tunneling states were derived. In addition, the torsional energy difference between both states could be accurately determined, being 23.9687 MHz. The non-observation of the cycloaddition reaction product is in agreement with our ab initio calculations and with previous results that concluded that the reactivity of CIs toward CO is measured to be quite limited., This research was supported by the Ministry of Science and Technology of Taiwan under Grant Nos MOST 104–2113–M–009– 020 (Y.E.) and MOST 105–2811–M–009–026 and 106–2811–M–0 09–023 (C.C.).

The reaction system between the simplest Criegee intermediate, CH

11 pags., 2 figs., 2 tabs., The microwave spectrum of the doubly deuterated cyanomethyl radical (DCCN) in its ground electronic state (B) has been observed for the lowest four rotational transitions (N = 1–0, 2–1, 2–1 and 2–1) using a Fourier transform microwave spectrometer in combination with a pulsed discharge nozzle. A total of 394 hyperfine components were measured and subjected to a least squares analysis which allowed determining twelve hyperfine constants for nitrogen and deuterium nuclei. With this new set of molecular constants we obtained accurate predictions for low N rotational transitions with hyperfine structure, and searched for this species in TMC–1., C. C. and J. C. thank to the European Research Council for fund-ing support under Synergy Grant ERC-2013-SyG, G.A. 610256 (NANOCOSMOS) and to Ministerio de Ciencia e Innovación for funding support through projects AYA2016–75066–C2–1–P andPID2019–107115GB–C21. Y. E. thanks Ministry of Science and Technology of Taiwan for funding support under grant MOST108–2113–M–009–25.

Our observations of TMC-1 with the Yebes 40 m radio telescope in the 31.0-50.3 GHz range allowed us to detect a group of unidentified lines, showing a complex line pattern indicative of an open-shell species. {}The observed frequencies of these lines and the similarity of the spectral pattern with that of the 2$_{0,2}$-1$_{0,1}$ rotational transition of H$_2$CCN indicate that the lines arise from the deuterated cyanomethyl radical, HDCCN. Using Fourier transform microwave spectroscopy experiments combined with electric discharges, we succeeded in producing the radical HDCCN in the laboratory and observed its 1$_{0,1}$-0$_{0,0}$ and 2$_{0,2}$-1$_{0,1}$ rotational transitions. From our observations and assuming a rotational temperature of 5 K, we derive an abundance ratio H$_2$CCN/HDCCN=20$\pm$4. The high abundance of the deuterated form of H$_2$CCN is well accounted for by a standard gas-phase model, in which deuteration is driven by deuteron transfer from the H$_2$D$^+$ molecular ion., Comment: This article was submitted to A&A Letters on 23/12/2020 and accepted for publication on 10/01/2021

12 pags., 6 figs., 7 tabs., Using the Yebes 40 m and IRAM 30 m radiotelescopes, we detected two series of harmonically related lines in space that can be fitted to a symmetric rotor. The lines have been seen towards the cold dense cores TMC-1, L483, L1527, and L1544. High level of theory ab initio calculations indicate that the best possible candidate is the acetyl cation, CH3CO+, which is the most stable product resulting from the protonation of ketene. We have produced this species in the laboratory and observed its rotational transitions Ju = 10 up to Ju = 27. Hence, we report the discovery of CH3CO+ in space based on our observations, theoretical calculations, and laboratory experiments. The derived rotational and distortion constants allow us to predict the spectrum of CH3CO+ with high accuracy up to 500 GHz. We derive an abundance ratio N(H2CCO)/N(CH3CO+) ∼44. The high abundance of the protonated form of H2CCO is due to the high proton affinity of the neutral species. The other isomer, H2CCOH+, is found to be 178.9 kJ mol-1 above CH3CO+. The observed intensity ratio between the K = 0 and K = 1 lines, ∼2.2, strongly suggests that the A and E symmetry states have suffered interconversion processes due to collisions with H and/or H2, or during their formation through the reaction of H3+ with H2CCO., The Spanish authors thank Ministerio de Ciencia e Innovación for funding support through project AYA2016-75066-C2-1-P, PID2019- 106235GB-I00 and PID2019-107115GB-C21/AEI/10.13039/501100011033. We also thank ERC for funding through grant ERC-2013-Syg-610256- NANOCOSMOS. MA and CB thanks Ministerio de Ciencia e Innovación for grants RyC-2014-16277 and FJCI-2016-27983, respectively. Y. Endo thanks Ministry of Science and Technology of Taiwan through grant MOST108-2113- M-009-25.

10 pags., 4 figs., 4 tabs., Context. The reaction between carbon atoms and vinyl cyanide, CH2CHCN, is a formation route to interstellar 3-cyano propargyl radical, CH2C3N, a species that has recently been discovered in space. The 1-cyano propargyl radical (HC3HCN), an isomer of CH2C3N, is predicted to be produced in the same reaction at least twice more efficiently than CH2C3N. Hence, HC3HCN is a plausible candidate to be observed in space as well. Aims. We aim to generate the HC3HCN radical in the gas phase in order to investigate its rotational spectrum. The derived spectroscopic parameters for this species will be used to obtain reliable frequency predictions to support its detection in space. Methods. The HC3HCN radical was produced by an electric discharge, and its rotational spectrum was characterized using a Balle-Flygare narrowband-type Fourier-transform microwave spectrometer operating in the frequency region of 4-40 GHz. The spectral analysis was supported by high-level ab initio calculations. Results. A total of 193 hyperfine components that originated from 12 rotational transitions, a- and b-type, were measured for the HC3HCN radical. The analysis allowed us to accurately determine 22 molecular constants, including rotational and centrifugal distortion constants as well as the fine and hyperfine constants. Transition frequency predictions were used to search for the HC3HCN radical in TMC-1 using the QUIJOTE survey between 30 and 50 GHz. We do not detect HC3HCN in TMC-1 and derive a 3σ upper limit to its column density of 6.0 × 1011 cm-2., The Spanish authors thank ERC for funding through grant ERC-2013-Syg-610256-NANOCOSMOS and Ministerio de Ciencia e Innovación for funding support through projects PID2019-106235GB-I00 and PID2019-107115GB-C21 / AEI / 10.13039/501100011033. M.A. thanks Ministerio de Ciencia e Innovación for grant RyC-2014-16277. Y.E. thanks Ministry of Science and Technology of Taiwan through grant MOST108-2113-M-009-25.

8 pags., 6 figs., 5 tabs., Criegee intermediates (CIs) are carbonyl oxides generated from ozonolysis of unsaturated hydrocarbons in the atmosphere. The relatively long lifetime of CIs makes possible the bimolecular reactions with other atmospheric agents. These reactions can potentially be fast enough to contribute significantly to the tropospheric budgets of those species or to alter the rate of generation of secondary organic aerosols (SOAs). In particular, the new adducts formed in these reactions contribute SOA formation because they have larger molecular weights and lower vapor pressures than the reactants and are more condensable. α-alkoxyalkyl hydroperoxides are the nascent products derived from the insertion reactions of CIs with alcohols. In this work we report the direct detection of methoxymethyl hydroperoxide (HOOCH2OCH3, MMHP) and methoxyethyl hydroperoxide (HOOC(CH3)HOCH3, MEHP) as the reaction products between the CIs, CH2OO and CH3CHOO and methanol. High resolution Fourier transform microwave spectroscopy has been used to identify one and two conformers of MMHP and MEHP, respectively. The pre-reactive complex CH2OO-CH3OH was not observed in this experiment, which indicates that CH2OO shows a different reactivity toward methanol than that toward water. Our results for CH3CHOO + CH3OH show that MEHP is produced in similar ratios when syn- and anti-CH3CHOO react with methanol vapor. This journal is, This research was supported by the Ministry of Science and Technology of Taiwan under Grant No. MOST 104-2113-M009-020 (Y. E.) and MOST 105-2811-M-009-026 and 106-2811- M-009-023 (C. C.).

The atmospheric reaction of the simplest Criegee intermediate, CH2OO, with formic acid has been investigated in the gas phase by pulsed Fourier-transform microwave spectroscopy. The dominant nascent product from this reaction was identified as hydroperoxymethyl formate (HOOCH2OCHO), for which two different conformations, formed through independent insertion mechanisms, were observed in the discharged plasma of a CH2I2/O2/formic acid gas mixture. The conformational identifications are supported by the observation of 13C species in natural abundance together with the chemically mono substituted deuterium isotopologues. These isotopic observations further suggest that hydroperoxymethyl formate slightly decomposes, producing formic anhydride (OHCOCHO) in a dehydration reaction.

The Criegee intermediates, carbonyl oxides produced in ozonolysis of unsaturated hydrocarbons, play important roles in atmospheric chemistry. The two conformers of CH3CHOO exhibit distinct reactivity toward several atmospheric species, but a distinct conformer-specific probe is challenging because ultraviolet and infrared absorption bands of syn- and anti-CH3CHOO overlap at low-resolution. Employing a quantum-cascade laser and a Herriott cell, we recorded the O–O stretching bands of CH2OO and syn-CH3CHOO in region 880–932 cm–1 at resolution 0.0015 cm–1. In addition to completely resolved vibration–rotational lines of CH2OO extending over 50 cm–1, some spectral lines associated with hot bands were identified. Spectral lines solely due to syn-CH3CHOO were also identified. Probing these lines, we determined the rate coefficient for the self-reaction of syn-CH3CHOO to be kself = (1.6 ± 0.60.5) × 10–10 cm3 molecule–1 s–1, about twice that of CH2OO.

Fourier transform microwave spectra for the J = 1 ← 0 and 2 ← 1 rotational transitions of the SiCl+ ion were observed for two isotopologues ( 35 Cl and 37 Cl) in the ground and the first excited vibrational states of the ground 1 Σ + electronic state. Thanks to the high resolution of the FTMW spectrometer, hyperfine structures due to the quadrupole moment of the chlorine nucleus and the nuclear spin-rotation interaction were fully resolved. The observed FTMW spectra were combined with previously reported MMW and diode laser spectra in an analysis to determine the mass-independent Dunham coefficients U k , l as well as a mass scaling parameter Δ 01 Cl = - 0.856 ( 30 ) . The equilibrium bond length of SiCl+ determined is r e = 1.9439729 ( 10 ) A and the nuclear quadrupole coupling constant of Si 35 Cl+ is eQq e = - 11.8788 ( 23 ) MHz.

We report the observation of a rotationally resolved ν6 band associated with the OO-stretching mode of the simplest Criegee intermediate, CH2OO, in the range of 879.5–932.0 cm−1 (11.37–10.73 μm) at an optical resolution of 0.0015 cm−1. The spectra were recorded with a tunable cw external-cavity quantum-cascade laser (EC-QCL) system coupled with a Herriott multipass absorption cell. Over one thousand lines were assigned to determine the rovibrational parameters of the ν6 band. Rotational parameters A′, B′, and C′ and higher-order parameters ΔJ, ΔJK, ΔK, δJ, and δK were determined precisely. Rotational perturbations for Ka′ = 3, Ka′ = 6, and Ka′ ≥ 11 on high-J levels were observed. In particular, for Ka′ = 6, frequency shifts as a function of J′ showed an avoided crossing; the shifts were analyzed in terms of a Coriolis interaction between modes ν6 and ν8 of CH2OO. According to the distinct temporal profiles, lines of a hot band near 899.5 cm−1 were also identified.

Experiments using pulsed Fourier-transform microwave spectroscopy have been performed to probe the reaction between the methyl substituted Criegee intermediate, CH3CHOO, and hydrogen chloride. Two conformers of the product derived from the insertion of HCl within CH3CHOO, chloroethyl hydroperoxide, formed in the discharged plasma of a CH3CHI2/O2/HCl gas mixture, were identified through their experimentally determined rotational and quadrupole coupling constants. The relative abundance of the detected species indicates that the reaction of the anti-CH3CHOO conformer is faster than that of the syn-CH3CHOO conformer. The results presented in this work constitute the first experimental information about the reaction between CH3CHOO and HCl.

Pulsed Fourier-transform microwave experiments have been performed to probe the products resulting from the reaction between HCl and the simplest Criegee intermediate, CH2 OO, where the reaction is considered to be important in atmospheric chemistry. The experimentally determined rotational parameters interpreted with the help of quantum chemical calculations support the identification of chloro-methyl hydroperoxide molecule as the primary product of this reaction.

6 pags., 3 figs., 6 tabs., Context. Nitriles constitute almost 15% of the molecules observed in the interstellar medium (ISM), surprisingly only two dinitriles have been detected in the ISM so far. The lack of astronomical detections for dinitriles may be partly explained by the absence of laboratory rotational spectroscopic data. Aims. Our goal is to investigate the rotational spectrum of glutaronitrile, NC-CH-CH-CH-CN, in order to allow its possible detection in the ISM. Methods. The rotational spectrum of glutaronitrile was measured using two different experimental setups. A Fourier transform microwave spectrometer was employed to observe the supersonic jet rotational spectrum of glutaronitrile between 6 and 20 GHz. In addition, the mmW spectrum was observed in the frequency range 72-116.5 GHz using a broadband millimetre-wave spectrometer based on radio astronomy receivers with fast Fourier transform backends. The spectral searches were supported by high-level ab initio calculations. Results. A total of 111 rotational transitions with maximum values of J and K quantum numbers 54 and 18, respectively, were measured for the gg conformer of glutaronitrile. The analysis allowed us to accurately determine the rotational, nuclear quadrupole coupling, quartic and sextic centrifugal distortion constants. These rotational parameters were employed to search for glutaronitrile in the cold and warm molecular clouds Orion KL, Sgr B2(N), B1-b and TMC-1, using the spectral surveys captured by IRAM 30 m at 3 mm. Glutaronitrile was not detected, and the upper limits' column densities were derived. Those are a factor of 1.5 and 5 lower than those obtained for the total column densities of the analogous succinonitrile in Orion KL and Sgr B2, respectively., We thank the European Research Council for funding support under Synergy Grant ERC-2013-SyG, G.A. 610256 (NANOCOSMOS). CB thanks to Ministerio de Ciencia, Innovación y Universidades for a Juan de la Cierva postdoctoral fellowship (FJCI-2016-27983). YE thanks to the Ministry of Science and Technology of Taiwan for the Grant MOST 104-2113-M-009- 020. This work was also based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Measurement of pure rotational transitions for the vinylthio radical, CH2CHS, previously observed by Fourier-transform microwave spectroscopy (Nakajima et al., 2007), are extended to a number of fine and hyperfine component lines split by the unpaired electron spin and the three non-equivalent protons. All the measured transition frequencies have been analyzed by a Hamiltonian for doublet asymmetric top molecules with hyperfine interaction terms for three nuclear spins, yielding precise molecular constants of CH2CHS in the ground state. Discussions on the electronic structure of CH2CHS are given based on the determined molecular constants.

74th ISMS 2019, University of Illinois, at Urbana-Champaign, June 17 - 21, 2019

Four conformers of the n-propyl-substituted Criegee intermediate, CH CH CH CHOO, also named n-butyraldehyde oxide, have been observed by Fourier transform microwave spectroscopy. The transient species was produced using a pulsed electric discharge of a gas mixture of 1,1-diiodobutane/O diluted in Ar or Ne. The observation of only syn species is in contrast to the results of other previous studies of alkyl-substituted Criegee intermediates, in particular, those for the structural isomers, isobutyraldehyde oxide ((CH ) CHCHOO), and methyl-ethyl-ketone oxide (C H C(CH )OO), for which syn and anti species have been observed coexisting in the gas phase., This research was supported by the Ministry of Science and Technology of Taiwan under Grant Nos MOST 104-2113-M-009-020 (Y.E.) and MOST 105-2811-M-009-026 and MOST 105- 2811-M-009-026 (C.C.). J.-C.G. thanks the Centre National d’Etudes Spatiales (CNES) and the Program PCMI (INSU-CNRS) for financial support.

8 pags., 8 figs., 5 tabs., We report the detection, for the first time in space, of cyano thioformaldehyde (HCSCN) and propynethial (HCSCCH) towards the starless core TMC-1. Cyano thioformaldehyde presents a series of prominent a- and b-type lines, which are the strongest previously unassigned features in our Q-band line survey of TMC-1. Remarkably, HCSCN is four times more abundant than cyano formaldehyde (HCOCN). On the other hand, HCSCCH is five times less abundant than propynal (HCOCCH). Surprisingly, we find an abundance ratio HCSCCH/HCSCN of ∼0.25, in contrast with most other ethynyl-cyanide pairs of molecules for which the CCH-bearing species is more abundant than the CN-bearing one. We discuss the formation of these molecules in terms of neutral-neutral reactions of S atoms with CH2CCH and CH2CN radicals as well as of CCH and CN radicals with H2CS. The calculated abundances for the sulphur-bearing species are, however, significantly below the observed values, which points to an underestimation of the abundance of atomic sulphur in the model or to missing formation reactions, such as ion-neutral reactions., This research has been funded by ERC through grant ERC-2013-Syg-610256-NANOCOSMOS. Authors also thank Ministerio de Ciencia e Innovación (Spain) for funding support through projects AYA2016-75066-C2-1-P, PID2019-106235GB-I00 and PID2019-107115GBC21/AEI/10.13039/501100011033. MA thanks Ministerio de Ciencia e Innovación for grant RyC-2014-16277. YE thanks Ministry of Science and Technology, Taiwan, for grant No. MOST 108-2113-M-009-025 and MOST 108- 2811-M-009-520.

The high resolution rotational spectroscopic observation of 1,1-diiodoethane is investigated using a pulsed jet, cavity Fourier transform microwave (FTMW) spectrometer over the frequency range 11.5–18 GHz for the first time. The rotational constants, the centrifugal distortion constants, the nuclear spin-rotation coupling constants, and the complete tensor components of the nuclear quadrupole coupling for both iodine nuclei have been determined and reported. The fitted rotational constants are A = 4548.320446(47), B = 625.629141(55), C = 558.798939(43) MHz and the nuclear quadrupole coupling constants are χaa = −1089.8125(7), χbb − χcc = −542.3162(13), |χab| = 1215.7505(10), χbc = 340.8983(14), and |χac| = 562.4206(19) MHz. No A-E splittings due to the methyl group internal rotation were observed. Many dipole-forbidden/electric quadrupole coupling allowed transitions were observed in the spectrum due to the large iodine quadrupole coupling effect. Quantum chemical calculations were performed at the CCSD(T)/aug-cc-pVTZ-pp level of theory. The calculated rotational constants, centrifugal distortion constants, and hyperfine constants were used to guide the data analysis.

We report the detection in TMC-1 of the protonated form of C3S. The discovery of the cation HC3S+ was carried through the observation of four harmonically related lines in the Q band using the Yebes 40m radiotelescope, and is supported by accurate ab initio calculations and laboratory measurements of its rotational spectrum. We derive a column density N(HC3S+) = (2.0 +/- 0.5)e11 cm-2, which translates to an abundance ratio C3S/HC3S+ of 65 +/- 20. This ratio is comparable to the CS/HCS+ ratio (35 +/- 8) and is a factor of about ten larger than the C3O/HC3O+ ratio previously found in the same source. However, the abundance ratio HC3O+/HC3S+ is 1.0 +/- 0.5, while C3O/C3S is just 0.11. We also searched for protonated C2S in TMC-1, based on ab initio calculations of its spectroscopic parameters, and derive a 3sigma upper limit of N(HC2S+) < 9e11 cm-2 and a C2S/HC2S+ > 60. The observational results are compared with a state-of-the-art gas-phase chemical model and conclude that HC3S+ is mostly formed through several pathways: proton transfer to C3S, reaction of S+ with c-C3H2, and reaction between neutral atomic sulfur and the ion C3H3+., Accepted for publication in A&A Letters

1 pag. -- Erratum: A&A 642, L17 (2020), https://doi.org/10.1051/0004-6361/202039351, IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain)

8 pags., 4 figs., 7 tabs., Using the Yebes 40m and IRAM 30m radio telescopes, we detected a series of harmonically related lines with a rotational constant B0 = 4460.590 ± 0.001 MHz and a distortion constant D0 = 0.511 ± 0.005 kHz towards the cold dense core TMC-1. High-level-of-theory ab initio calculations indicate that the best possible candidate is protonated tricarbon monoxide, HC3O+. We have succeeded in producing this species in the laboratory and observed its Ju-Jl = 2-1 and 3-2 rotational transitions. Hence, we report the discovery of HC3O+ in space based on our observations, theoretical calculations, and laboratory experiments. We derive an abundance ratio N(C3O)/N(HC3O+) ∼7. The high abundance of the protonated form of C3O is due to the high proton affinity of the neutral species. The chemistry of O-bearing species is modelled, and predictions are compared to the derived abundances from our data for the most prominent O-bearing species in TMC-1., The Spanish authors thank Ministerio de Ciencia e Innovación for funding support through projects AYA2016-75066-C2-1-P, PID2019-107115GB-C21. We also thank ERC for funding through Grant ERC-2013-Syg-610256-NANOCOSMOS. M. A. and C. B. thanks MICIN for grants RyC-2014-16277 and FJCI-2016-27983, respectively. Y. Endo thanks Ministry of Science and Technology of Taiwan through Grant MOST108-2113- M-009-25.

Pure rotational transitions of three conformers of epichlorohydrin were observed. Among the three possible conformers expected for this species, spectra of the two chlorine isotopologues, 35Cl and 37Cl, have been detected for the two gauche-conformers, while only the 35Cl isotopologue was detected for the cis-conformer which is much higher in energy. Well resolved chlorine nuclear hyperfine splittings were observed for all the conformers and isotopologues, yielding precisely determined molecular constants.

10 pags., 5 figs., 7 tabs., 5 apps., We report on the detection of two series of harmonically related doublets in IRC+10216. From the observed frequencies, the rotational constant of the first series is B = 1380.888 MHz and that of the second series is B = 1381.512 MHz. The two series correspond to two species with a 2Σ electronic ground state. After considering all possible candidates, and based on quantum chemical calculations, the first series is assigned to MgC3N and the second to MgC4H. For the latter species, optical spectroscopy measurements support its identification. Unlike diatomic metal-containing molecules, the line profiles of the two new molecules indicate that they are formed in the outer layers of the envelope, as occurs for MgNC and other polyatomic metal-cyanides. We also confirm the detection of MgCCH that was previously reported from the observation of two doublets. The relative abundance of MgC3N with respect to MgNC is close to one while that of MgC4H relative to MgCCH is about ten. The synthesis of these magnesium cyanides and acetylides in IRC+10216 can be explained in terms of a two-step process initiated by the radiative association of Mg+ with large cyanopolyynes and polyynes followed by the dissociative recombination of the ionic complexes., The Spanish authors thank the Ministerio de Ciencia Innovación y Universidades for funding support from the CONSOLIDER-Ingenio program “ASTROMOL” CSD 2009-00038, AYA2012-32032, AYA2016-75066-C2-1-P. We also thank ERC for funding through grant ERC-2013-Syg610256-NANOCOSMOS. MA thanks the Ministerio de Ciencia Innovación y Universidades for the Ramón y Cajal grant RyC-2014-16277. CB thanks the Ministerio de Ciencia Innovación y Universidades for the Juan de la Cierva grant FJCI-2016-27983. LVP acknowledges support from the Swedish Research Council and from ERC consolidator grant 614

In a previous work, Cabezas et al., 2017 [21], we reported the rotational study of the doubly substituted methyl-ethyl Criegee intermediate, C2H5C(CH3)OO, by using Fourier transform microwave spectroscopy. Four different conformers were found showing A/E splittings due to the internal rotation of methyl tops. However for one of the conformers, syn2, some of the observed lines showed additional splitting that could not be assigned. The present work has been aimed to shed light on these transition line splittings of the syn2 conformer which are assigned to additional splittings coming from the two nonequivalent tops. As a consequence, 182 lines have been observed and the analysis of the internal rotation motions of two non-equivalent methyl tops enabled us to determine the barrier heights of the hindered methyl rotation of the two tops.

Pure rotational transitions of the anti-form of the simplest alkyl-substituted Criegee intermediate, anti-CH3CHOO, were observed by Fourier-transform microwave spectroscopy. The observed transition frequencies in the A and E levels of the ground vibrational state were analyzed together, and molecular constants including parameters which characterize the internal rotation of the methyl rotor were determined. The experimentally determined barrier height of the three-fold potential for the methyl internal rotation is 399.1 cm−1, less than a half of that of the other conformer, syn-CH3CHOO (Nakajima and Endo, 2014).

Pure rotational transitions of the simplest Criegee intermediate, CH2OO, were observed for several excited vibrational levels by Fourier-transform microwave spectroscopy combined with a double-resonance technique, and precise rotational constants of vibrationally excited CH2OO were determined. Comparing the experimentally determined vibration–rotation constants with those derived from a high-level ab initio potential energy surface, vibrational assignments were made for the observed levels. The observed intensities of the 101–000 rotational lines suggested that the COO bending mode is significantly excited.