Search

Context. The carbamoyl radical (H2NCO) is believed to play a central role in the ice-grain chemistry of crucial interstellar complex organic molecules such as formamide and acetamide. Yet, little is known about this radical, which remains elusive in laboratory gasphase experiments. Aims. In order to enable interstellar searches of H2NCO, we have undertaken a mandatory laboratory characterisation of its pure rotational spectrum. Methods. We report the gas-phase laboratory detection of H2NCO, produced by H-atom abstraction from formamide, using pure rotational spectroscopy at millimetre and submillimetre wavelengths. Millimetre-wave data were acquired using chirped-pulse Fourier-transform spectroscopy, while submillimetre-wave ones were obtained using Zeeman-modulated spectroscopy. Experimental measurements were guided by quantum-chemical calculations at the ωB97X-D/cc-pVQZ level of theory. Interstellar searches for the radical have been undertaken in the Protostellar Interferometric Line Survey (PILS) towards the solar-type protostar IRAS 16293-2422. Results. From the assignment and fit of experimental transitions up to 660 GHz, reliable spectroscopic parameters for H2NCO in its ground vibrational state have been derived, enabling accurate spectral predictions. No transitions of the radical were detected in the PILS survey. The inferred upper limit shows that the H2NCO abundance is at least 60 times below that of formamide and 160 times below that of HNCO in this source; a value that is in agreement with predictions from a physico-chemical model of this young protostar. [ABSTRACT FROM AUTHOR]

Owing to its unparalleled structural specificity, rotational spectroscopy is a powerful technique to unambiguously identify and characterize volatile, polar molecules. We present here a new experimental approach, automated microwave double resonance (AMDOR) spectroscopy, to rapidly determine the rotational constants of these compounds without a priori knowledge of elemental composition or molecular structure. This task is achieved by rapidly acquiring the classical (frequency vs. intensity) broadband spectrum of a molecule using chirped-pulse Fourier transform microwave (FTMW) spectroscopy and subsequently analyzing it in near real-time using complementary cavity FTMW detection and double resonance. AMDOR measurements provide a unique "barcode" for each compound from which rotational constants can be extracted. To illustrate the power of this approach, AMDOR spectra of three aroma compounds - trans-cinnamaldehyde, α-, and β-ionone - have been recorded and analyzed. The prospects to extend this approach to mixture characterization and purity assessment are described. [ABSTRACT FROM AUTHOR]

Rotational spectroscopy is an invaluable tool to unambiguously determine the molecular structure of a species, and sometimes even to establish its very existence. This article illustrates how experimental and theoretical state‐of‐the‐art tools can be used in tandem to investigate the rotational structure of molecules, with particular emphasis on those that have long remained elusive. The examples of three emblematic species—gauche‐butadiene, disilicon carbide, and germanium dicarbide—highlight the close, mutually beneficial interaction between high‐level theoretical calculations and sensitive microwave measurements. Prospects to detect other elusive molecules of chemical and astronomical interest are discussed. [ABSTRACT FROM AUTHOR]

We report the gas-phase detection and spectroscopic characterisation of ethynethiol (), a metastable isomer of thioketene () using a combination of Fourier-transform microwave and submillimetre-wave spectroscopies. Several a-type transitions of the normal species were initially detected below 40 GHz using a supersonic expansion-electrical discharge source, and subsequent measurement of higher-frequency, b-type lines using double resonance provided accurate predictions in the submillimetre region. With these, searches using a millimetre-wave absorption spectrometer equipped with a radio frequency discharge source were conducted in the range 280–660 GHz, ultimately yielding nearly 100 transitions up to and. From the combined data set, all three rotational constants and centrifugal distortion terms up to the sextic order were determined to high accuracy, providing a reliable set of frequency predictions to the lower end of the THz band. Isotopic substitution has enabled both a determination of the molecular structure of HCCSH and, by inference, its formation pathway in our nozzle discharge source via the bimolecular radical-radical recombination reaction , which is calculated to be highly exothermic (−477 kJ/mol) using the HEAT345(Q) thermochemical scheme. [ABSTRACT FROM AUTHOR]

Abstract: The planarity of the second stable conformer of 1,3‐butadiene, the archetypal diene for the Diels–Alder reaction in which a planar conjugated diene and a dienophile combine to form a ring, is not established. The most recent high level calculations predicted the species to adopt a twisted, gauche structure owing to steric interactions between the inner terminal hydrogens rather than a planar, cis structure favored by the conjugation of the double bonds. The structure cis‐1,3‐butadiene is unambiguously confirmed experimentally to indeed be gauche with a substantial dihedral angle of 34°, in excellent agreement with theory. Observation of two tunneling components indicates that the molecule undergoes facile interconversion between two equivalent enantiomeric forms. Comparison of experimentally determined structures for gauche‐ and trans‐butadiene provides an opportunity to examine the effects of conjugation and steric interactions. [ABSTRACT FROM AUTHOR]

Abstract: The planarity of the second stable conformer of 1,3‐butadiene, the archetypal diene for the Diels–Alder reaction in which a planar conjugated diene and a dienophile combine to form a ring, is not established. The most recent high level calculations predicted the species to adopt a twisted, gauche structure owing to steric interactions between the inner terminal hydrogens rather than a planar, cis structure favored by the conjugation of the double bonds. The structure cis‐1,3‐butadiene is unambiguously confirmed experimentally to indeed be gauche with a substantial dihedral angle of 34°, in excellent agreement with theory. Observation of two tunneling components indicates that the molecule undergoes facile interconversion between two equivalent enantiomeric forms. Comparison of experimentally determined structures for gauche‐ and trans‐butadiene provides an opportunity to examine the effects of conjugation and steric interactions. [ABSTRACT FROM AUTHOR]

Supercritical CO2 is an appealing nontoxic, environmentally friendly solvent for the industrial extraction of many classes of compounds, from caffeine to natural product drug precursors to petrochemical impurities. Apolar in isolation, the ability of supercritical CO2 to dissolve polar species has been empirically shown to be greatly enhanced by the addition of a small molar percentage of a polar cosolvent, often ethanol. Computational work predicts that the isolated ethanol-CO2 complex can exist either in an electron-donor configuration or through a hydrogen-bonding one; yet, neither has been previously experimentally observed. Here, we demonstrate by rotational spectroscopy that the isolated, gas-phase ethanol-CO2 dimer is an electron donor-acceptor complex. [ABSTRACT FROM AUTHOR]

C 3 , a pure carbon chain molecule that has been identified in different astronomical environments, is considered a good probe of kinetic temperatures through observation of transitions involving its low-lying bending mode (ν 2) in its ground electronic state. The present laboratory work aims to investigate this bending mode with multiple quanta of excitation by combining recordings of high resolution optical and infrared spectra of C 3 produced in discharge experiments. The optical spectra of rovibronic ( A ̃ 1 Π u − X ̃ 1 Σ g + ) transitions have been recorded by laser induced fluorescence spectroscopy using a single longitude mode optical parametric oscillator as narrow bandwidth laser source at the University of Science and Technology of China. 36 bands originating from X ̃ (0 v 2 0), v 2 = 0 − 5 , are assigned. The mid-infrared spectrum of the rovibrational ν 3 band has been recorded by Fourier-transform infrared spectroscopy using a globar source on the AILES beamline of the SOLEIL synchrotron facility. The spectrum reveals hot bands involving up to 5 quanta of excitation in ν 2. From combining analyses of all the presently recorded spectra and literature data, accurate rotational parameters and absolute energy levels of C 3 , in particular for states involving the bending mode, are determined. A single PGOPHER file containing all available data involving the X ̃ and A ̃ states (literature and present study) is used to fit all the data. The spectroscopic information derived from this work enables new interstellar searches for C 3 , not only in the infrared and optical regions investigated here but also notably in the ν 2 band region (around 63 cm − 1) where vibrational satellites can now be accurately predicted. This makes C 3 a universal diagnostic tool to study very different astronomical environments, from dark and dense to translucent clouds. [Display omitted] • Most complete spectroscopic description of the C 3 molecule to date. • Combination of infrared and optical laboratory data. • PGOPHER fit of this work and literature data. [ABSTRACT FROM AUTHOR]

Thionitrous acid (HSNO), a potential key intermediate in biological signaling pathways, has been proposed to link NO and H2S biochemistries, but its existence and stability in vivo remain controversial. We establish that HSNO is spontaneously formed in high concentration when NO and H2S gases are mixed at room temperature in the presence of metallic surfaces. Our measurements reveal that HSNO is formed by the reaction H2S + N2O3 → HSNO + HNO2, where N2O3 is a product of NO disproportionation. These studies also suggest that further reaction of HSNO with H2S may form HNO and HSSH. The length of the S-N bond has been derived to high precision and is found to be unusually long: 1.84 Å, the longest S-N bond reported to date for an R-SNO compound. The present structural and, particularly, reactivity investigations of this elusive molecule provide a firm foundation to better understand its potential physiological chemistry and propensity to undergo S-N bond cleavage in vivo. [ABSTRACT FROM AUTHOR]

The high resolution Fourier-transform spectrum of acrylonitrile covering the 40–700 cm −1 spectral region was recorded at the AILES infrared beamline of the SOLEIL synchrotron. The spectrum allowed assignment of vibration–rotation transitions in four different fundamental bands, five hot bands, one overtone band, as well as of some pure rotational transitions. The new infrared data and previous measurements made with microwave techniques have been combined into a single global fit encompassing over 31 000 measured transitions. Precise vibrational term values have been determined for the eight lowest excited vibrational states, including ν 11 = 228.299930(4), ν 15 = 332.678207(4), ν 10 = 560.716701(5), and ν 14 = 681.793862 ( 13 ) cm −1 . The new values are compared with those obtained previously entirely on the basis of rotational perturbations. Several anharmonicity coefficients are determined and compared with ab initio anharmonic force field calculations. The assignment of the ν 10 mode is also clarified. [ABSTRACT FROM AUTHOR]

Thionyl chloride (SOCl 2 ) is a volatile inorganic compounds used extensively in industry. Its monitoring in gas phase is critical both for environmental and defense concerns. Previous high-resolution gas phase spectroscopic studies were focused on the microwave region (below 40 GHz) and no rotationally-resolved study of the IR spectrum has been reported to date. We present in this article a rovibrational analysis of the two lowest frequency infrared active bending modes ν 3 and ν 6 of SOCl 2 . By means of synchrotron based Fourier-Transform far-infrared spectroscopy on the AILES beamline of the SOLEIL facility, the spectra of the symmetric ν 3 (346 cm −1 ) and asymmetric ν 6 (283 cm −1 ) fundamental bands have been rotationally resolved and analyzed. [ABSTRACT FROM AUTHOR]

We report high temperature spectroscopic measurements of water vapor carried out in the far infrared domain. The new data set contains numerous transitions characterized by a J -value larger than 30 and allows us to reach rotational levels of water for which information was either unavailable or inaccurate. This new data set, along with previously published microwave, far infrared, and infrared measurements, is fitted using a modified version of the Bending–Rotation approach and allows us to perform the first analysis of the high-resolution spectrum of water vapor up to J = 30 for the ground and (0 1 0) states, up to J = 27 for the First Triad States, and up to J = 19 for the Second Triad States. The results of the analysis are used to build a spectroscopic database supporting high-resolution investigations performed at temperatures as high as 1500 K. [ABSTRACT FROM AUTHOR]

[Display omitted] A combination of millimeter-wave and high-resolution infrared data is used to analyze the eight lowest-energy vibrational states of benzonitrile (C 6 H 5 CN, C 2 v , μ a = 4.5 D), a benzene derivative recently detected in the interstellar medium. The overtone states v 22 = 2 and v 33 = 2, combination state v 22 = 1, v 33 = 1, and fundamental states v 21 = 1 and v 15 = 1 are studied for the first time by rotationally resolved spectroscopy. The three former states form a Coriolis- and Darling-Dennison-coupled triad of interacting states for which the coupling terms and highly precise, deperturbed energy separations have been measured. The use of sub-millimeter and far-infrared data together enabled the determination of the purely rotational and coupling parameters for the six lowest-energy vibrationally excited states of benzonitrile, along with their highly precise energies (E 22 = 141.4810252 (57) cm−1, E 33 = 160.5891953 (47) cm−1, E 2×22 = 282.6295417 (83) cm−1, E 22+33 = 302.5795909 (87) cm−1, E 2×33 = 321.4923856 (77) cm−1, E 21 = 372.257993 (10) cm−1). These energies, the resultant experimental anharmonicity constants (x 22,22 = − 0.1663 cm−1, x 33,33 = 0.1570 cm−1, and x 22,33 = 0.4909 cm−1), and semi-experimental harmonic frequencies (ω 22 = 142.9 cm−1 and ω 33 = 161.0 cm−1) for the ν 22 and ν 33 states are compared to CCSD(T)/ANO1 predicted values. The spectroscopic and coupling constants determined in this work for the vibrational ground state, the two lowest-energy fundamental states, and the corresponding first overtone and combination states successfully predict experimental frequencies down to 8 GHz. Particularly for the vibrationally excited states, the ability to predict transition frequencies so far outside the frequency region in which the constants were determined confirms that the rotational and distortion constants, as well as the coupling terms, are determined reasonably close to their true values. The ability to accurately extrapolate also demonstrates the suitability of the determined constants as the basis for extraterrestrial identification and examination of these vibrational states of benzonitrile. [ABSTRACT FROM AUTHOR]

Abstract: A continuous-wave terahertz (CW-THz) source generated by photomixing has been employed to detect and quantify radicals produced in a cold plasma probing their spin-rotation transitions. Due to their dual interest for both atmospherists and astrophysicists, the hydroxyl OH and the mercapto SH radicals have been chosen. The photomixing technique which can access the largest range of THz frequencies of any known coherent source, allowed to resolve the Doppler-limited hyperfine transitions of OH in the 2.5THz frequency region. Line profile analysis of the hyperfine components demonstrated that OH radicals have been detected in this region at a ppm level at a temperature close to 490K. The hyperfine structure of SH has been resolved for the first time above 1THz. Ten new frequency transitions have been measured in the 1.3–2.6THz frequency range using the CW-THz synthesizer based on a frequency comb. With relative uncertainties better than 10−7, the CW-THz frequencies measured in this study are now competitive with those measured by other instruments such as frequency multiplication chains or FT-FIR spectrometers and are now capable to improve the predictions of the complete high-resolution spectra of these radicals collected in the atmospheric and astrophysical spectroscopic databases. versioncorrigeeAC 2011-07-18 17:32 © 2011 Arnaud Cuisset. [Copyright &y& Elsevier]

[Display omitted] • cyanoadamantane and isocyanoadamantane have been characterized in the gas phase. • Their medium resolution far- and mid-infrared spectra have been measured. • Rotational transitions have been recorded in the millimeter-wave domain. • Quantum chemistry has been used to guide spectroscopic assignments. Because of their high stability, the presence of diamond-type molecules has long been suspected in the interstellar medium, a hypothesis supported by the extraction of diamond nanocrystal from some meteorites. We report the rotational and vibrational investigation of two polar derivatives of adamantane (C 10 H 16), 1-cyanoadamantane (C 10 H 15 –CN) and 1-isocyanoadamantane (C 10 H 15 –NC), using room temperature gas phase absorption spectroscopy. Pure rotational spectra have been recorded at millimeter wavelengths (75–220 GHz) while vibrational spectra were obtained in the far- and mid-infrared domains (50–3500 cm−1). Quantum chemical calculations have been performed on these two C 3 v rotors to support the spectral analysis enabling the assignment, for both species, of more than 7000 pure rotational transitions in the ground (A 1 symmetry) and first vibrationally excited (E symmetry) states, and of most of the infrared active bands. The pure rotational lines were fit to their experimental accuracy using a symmetric-top Hamiltonian. Our study provides all necessary information for an active search of these species in space. [ABSTRACT FROM AUTHOR]

• First high-resolution infrared study of ethyl cyanid. • Four energetically lowest vibrational fundamentals studied. • Global fits of infrared and pure rotational spectra performed. • Strong vibrational satellites towards high mass star forming region assigned. The high resolution vibrational spectrum of ethyl cyanide (C 2 H 5 CN) has been investigated in the far-IR using synchrotron-based Fourier transform spectroscopy. The assignment was performed using the Automated Spectral Assignment Procedure (ASAP) allowing accurate rotational energy levels of the four lowest fundamental vibrations of the species, namely the v 13 = 1 @ 205.934099(8) cm−1, v 21 = 1 @ 212.141101(8) cm−1, v 20 = 1 @ 372.635293(15) cm−1, and v 12 = 1 @ 532.699617(16) cm−1 states, to be determined. The analysis not only confirms the applicability of the ASAP in the treatment of (dense) high-resolution infrared spectra but also reveals some of its limitations. Complementary to the infrared study, the pure rotational spectrum of C 2 H 5 CN was also studied in selected frequency ranges from 75 to 255 GHz. New observations of a prototypical high-mass star-forming region, G327.3–0.6, performed with the Atacama Large Millimeter Array show that vibrational satellites of C 2 H 5 CN can be very intense, of order several tens of Kelvin in units of brightness temperature. [ABSTRACT FROM AUTHOR]

A systematic search for carbon-chain cumulenones beyond H2C4O has been undertaken using microwave spectral taxonomy in combination with a pulsed jet discharge source. No evidence was found for the C2V isomer of H2C5O or its longer derivatives, but HC(O)C4H, the longer variant of propynal, HC(O)CCH, was identified instead. Its rotational and leading centrifugal distortion constants have been derived to high accuracy from detection of both a- and b-type lines; those below 40 GHz were measured using a Fabry-Perot cavity, while lines between 40 and 72 GHz were recorded by double resonance techniques. Overwhelming evidence for the identification is provided by detection of HC(O)C4D, DC(O)C4H, and HC(18O)C4H at the expected frequencies using isotopically enriched samples. Because HC(18O)C4H is produced with comparable abundance when using either 18O2 or C18O as the source of oxygen, and because H13C(O)C4H is not preferentially formed when starting from 13CO, atomic oxygen appears to be a key reactant in formation, plausibly viaOinsertion, e.g., H2CC2n+2H + O → HC(O)C2n+2H + H. Under the same experimental conditions, HC(O)CCH is more than 10 times more abundant than H2C3O, regardless of the source of oxygen, and no evidence is found for cyclopropenone, c-C3H2O. Taken together, these observations indicate that propynal and longer chains with an odd number of carbon atoms are either energetically more stable than cumulenones of the same size, are kinetically favored products, or both. On the basis of the HC(O)C4H discovery, searches for the isovalent sulfur species, HC(S)C4H, and HC(O)C6H have been conducted. Guided by new quantum chemical calculations, the rotational spectra of both were observed in the centimeter-wave band with the same spectrometer. [ABSTRACT FROM AUTHOR]

A steady state concentration of HSNO is obtained using a gaseous mixture of 1% NO and 0.1% H2S in Ne by supersonic expansion into a cavity through a pulsed valve at 25 °C. [ABSTRACT FROM AUTHOR]

A steady state concentration of HSNO is obtained using a gaseous mixture of 1% NO and 0.1% H2S in Ne by supersonic expansion into a cavity through a pulsed valve at 25 °C. [ABSTRACT FROM AUTHOR]

The ν2 and ν5 fundamental bands of thionyl chloride (SOCl2) were measured in the 420 cm-1-550 cm-1 region using the FT-far-IR spectrometer exploiting synchrotron radiation on the AILES beamline at SOLEIL. A straightforward line-by-line analysis is complicated by the high congestion of the spectrum due to both the high density of SOCl2 rovibrational bands and the presence of the ν2 fundamental band of sulfur dioxide produced by hydrolysis of SOCl2 with residual water. To overcome this difficulty, our assignment procedure for the main isotopologues 32S16O35Cl2 and 32S16O35Cl37Cl alternates between a direct fit of the spectrum, via a global optimization technique, and a traditional line-by-line analysis. The global optimization, based on an evolutionary algorithm, produces rotational constants and band centers that serve as useful starting values for the subsequent spectroscopic analysis. This work helped to identify the pure rotational submillimeter spectrum of 32S16O35Cl2 in the v2 = 1 and v5 = 1 vibrational states of Martin-Drumel et al. [J. Chem. Phys. 144, 084305 (2016)]. As a by-product, the rotational transitions of the v4 = 1 far-IR inactive state were identified in the submillimeter spectrum. A global fit gathering all the microwave, submillimeter, and far-IR data of thionyl chloride has been performed, showing that no major perturbation of rovibrational energy levels occurs for the main isotopologue of the molecule. [ABSTRACT FROM AUTHOR]

HOCO is an important intermediate in combustion and atmospheric processes because the OH + CO → H + CO2 reaction represents the final step for the production of CO2 in hydrocarbon oxidation, and theoretical studies predict that this reaction proceeds via various intermediates, the most important being this radical. Isotopic investigations of trans- and cis-HOCO have been undertaken using Fourier transform microwave spectroscopy and millimeter-wave double resonance techniques in combination with a supersonic molecular beam discharge source to better understand the formation, chemical bonding, and molecular structures of this radical pair. We find that trans- HOCO can be produced almost equally well from either OH + CO or H + CO2 in our discharge source, but cis-HOCO appears to be roughly two times more abundant when starting from H + CO2. Using isotopically labelled precursors, the OH + C18O reaction predominately yields HOC18O for both isomers, but H18OCO is observed as well, typically at the level of 10%-20% that of HOC18O; the opposite propensity is found for the 18OH + CO reaction. DO + C18O yields similar ratios between DOC18O and D18OCO as those found for OH + C18O, suggesting that some fraction of HOCO (or DOCO) may be formed from the back-reaction H + CO2, which, at the high pressure of our gas expansion, can readily occur. The large 13C Fermi-contact term (aF) for trans- and cis-HO13CO implicates significant unpaired electronic density in a σ-type orbital at the carbon atom, in good agreement with theoretical predictions. By correcting the experimental rotational constants for zero-point vibration motion calculated theoretically using second-order vibrational perturbation theory, precise geometrical structures have been derived for both isomers. [ABSTRACT FROM AUTHOR]

Complete and reliable knowledge of the ammonia spectrum is needed to enable the analysis and interpretation of astrophysical and planetary observations. Ammonia has been observed in the interstellar medium up to J=18 and more highly excited transitions are expected to appear in hot exoplanets and brown dwarfs. As a result, there is considerable interest in observing and assigning the high J (rovibrational) spectrum. In this work, numerous spectroscopic techniques were employed to study its high J transitions in the ground and ν2=1 states. Measurements were carried out using a frequency multiplied submillimeter spectrometer at Jet Propulsion Laboratory (JPL), a tunable far-infrared spectrometer at University of Toyama, and a high-resolution Bruker IFS 125 Fourier transform spectrometer (FTS) at Synchrotron SOLEIL. Highly excited ammonia was created with a radiofrequency discharge and a dc discharge, which allowed assignments of transitions with J up to 35. One hundred and seventy seven ground state and ν2=1 inversion transitions were observed with microwave accuracy in the 0.3-4.7 THz region. Of these, 125 were observed for the first time, including 26 ΔK=3 transitions. Over 2000 far-infrared transitions were assigned to the ground state and ν2=1 inversion bands as well as the ν2 fundamental band. Of these, 1912 were assigned using the FTS data for the first time, including 222 ΔK=3 transitions. The accuracy of these measurements has been estimated to be 0.0003-0.0006 cm-1. A reduced root mean square error of 0.9 was obtained for a global fit of the ground and ν2=1 states, which includes the lines assigned in this work and all previously available microwave, terahertz, far-infrared, and mid-infrared data. The new measurements and predictions reported here will support the analyses of astronomical observations by high-resolution spectroscopy telescopes such as Herschel, SOFIA, and ALMA. The comprehensive experimental rovibrational energy levels reported here will permit further refinement of the potential energy surface to improve ammonia ab initio calculations and facilitate assignment of new high-resolution spectra of hot ammonia. [ABSTRACT FROM AUTHOR]

Sulfur monoxide (SO) is a highly reactive molecule and thus, eludes bulk isolation. We report here on synthesis and reactivity of a molecular precursor for SO generation, namely 7-sulfinylamino- 7-azadibenzonorbornadiene (1). This compound has been shown to fragment readily driven by dinitrogen expulsion and anthracene formation on heating in the solid state and in solution, releasing SO at mild temperatures (<100 °C). The generated SO was detected in the gas phase by MS and rotational spectroscopy. In solution, 1 allows for SO transfer to organic molecules as well as transition metal complexes. [ABSTRACT FROM AUTHOR]

Dibenzo-7-phosphanorbornadiene Ph3PC(H)PA (1, A = C14H10, anthracene) is reported here as a molecular precursor to phosphaethyne (HC≡P), produced together with anthracene and triphenylphosphine. HCP generated by thermolysis of 1 has been observed by molecular beam mass spectrometry, laser-induced fluorescence, microwave spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. In toluene, fragmentation of 1 has been found to proceed with activation parameters of ΔH⧧ = 25.5 kcal/mol and ΔS⧧ = -2.43 eu and is accompanied by formation of an orange insoluble precipitate. Results from computational studies of the mechanism of HCP generation are in good agreement with experimental data. This high-temperature method of HCP generation has pointed to new reaction chemistry with azide anion to produce the 1,2,3,4-phosphatriazolate anion, HCPN3-, for which structural data have been obtained in a single-crystal X-ray diffraction study. Negative-ion photoelectron spectroscopy has shown the adiabatic detachment energy for this anion to be 3.555(10) eV. The aromaticity of HCPN3- has been assessed using nucleus-independent chemical shift, quantum theory of atoms in molecules, and natural bond orbital methods. [ABSTRACT FROM AUTHOR]

Abstract: Pure rotational transitions of hydrogen sulfide (H2S) in its ground and first excited vibrational states have been recorded at room temperature. The spectrum comprises an average of 1020 scans at 0.005cm−1 resolution recorded in the region 45–360cm−1 (1.4 to 10.5THz) with a globar continuum source using a Fourier transform spectrometer located at the AILES beamline of the SOLEIL synchrotron. Over 2400 rotational lines have been detected belonging to ground vibrational state transitions of the four isotopologues H2 32S, H2 33S, H2 34S, and H2 36S observed in natural abundance. 65%of these lines are recorded and assigned for the first time, sampling levels as high as J=26 and K a =17 for H2 32S. 320 pure rotational transitions of H2 32S in its first excited bending vibrational state are recorded and analysed for the first time and 86 transitions for H2 34S, where some of these transitions belong to new experimental energy levels. Rotational constants have been fitted for all the isotopologues in both vibrational states using a standard effective Hamiltonian approach. Comprehensive comparisons are made with previously available data as well as the data available in HITRAN, CDMS, and JPL databases. The 91 transitions assigned to H2 36S give the first proper characterization of its pure rotational spectrum. [Copyright &y& Elsevier]

• Far-infrared spectrum of cyanoacetylene recorded for the first time. • 24 newly observed ro-vibrational bands. • About 17000 experimental transitions analyzed for 22 states. • Anharmonic resonances fully accounted for the 2nd polyad system around 1100 cm-1. • Rotational and ro-vibrational line list up to 3360 cm-1. • Rotational and ro-vibrational global analysis. The far-infrared spectrum of HC 3 N has been recorded at high resolution between 70 and 500 cm − 1 using synchrotron radiation. Four prominent features, i.e., ν 7 , ν 6 − ν 7 , ν 4 − ν 6 , and 2 ν 7 have been identified in the spectrum together with many associated hot bands. In addition, rotational transitions for the interacting v 4 = v 7 = 1 , (v 6 = 2 , v 7 = 1) , (v 5 = 1 , v 7 = 2) , and v 7 = 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 HC 3 N 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. [ABSTRACT FROM AUTHOR]

Abstract: Terahertz absorption spectroscopy and far infrared Fourier transform (FIR-FT) emission spectroscopy were employed to measure new rotational and ro-vibrational spectra and validate existing datasets for high temperature water, with the goal to improve the accuracy of predictions for pure rotation in the (020), (100) and (001) vibrational states. A total of 104 new rotational transitions in (000), (010), (020), (100) and (001) were observed in the 293–2723GHz region with MW accuracy and with observed J(Max)=18, 11, 10, 14, 10; K a (Max)=10, 7, 7, 7, 4; E″(Max)=4178, 3771, 4996, 5430, 4939 cm−1, respectively. A total of 4194 new FIR-FT transitions were assigned in the 50–600cm−1 region to the same five vibrational states with estimated experimental uncertainty of 0.0008–0.002cm−1 and with J(Max)=27; K a (Max)=21, 18, 18, 17, 17, respectively. Together with previous high-resolution observations, these new data were fitted with the Bending–Rotation approach and the Euler Hamiltonian. The new measurements and predictions reported here will support the analyses of astronomical observations by high-resolution spectroscopy telescopes such as Herschel, SOFIA, and ALMA. [Copyright &y& Elsevier]

Catechol is an oxygenated aromatic volatile organic compound and a biogenic precursor of secondary organic aerosols. Monitoring this compound in the gas phase is desirable due to its appreciable reactivity with tropospheric ozone. From a molecular point of view, this molecule is attractive since the two adjacent hydroxy groups can interchangeably act as donor and acceptor in an intramolecular hydrogen bonding due to the tunnelling between two symmetrically equivalent structures. Using synchrotron radiation, we recorded a rotationally-resolved Fourier Transform far-infrared (IR) spectrum of the torsional modes of the free and bonded -OH groups forming the intramolecular hydrogen bond. Additionally, the room temperature, pure rotational spectrum was measured in the 70–220 GHz frequency range using a millimeter-wave spectrometer. The assignment of these molecular transitions was assisted by anharmonic high-level quantum-chemical calculations. In particular, pure rotational lines belonging to the ground and the four lowest energy, vibrationally excited states were assigned. Splitting due to the tunnelling was resolved for the free -OH torsional state. A global fit combining the far-IR and millimeter-wave data provided the spectroscopic parameters of the low-energy far-IR modes, in particular those characterizing the intramolecular hydrogen bond dynamics. [ABSTRACT FROM AUTHOR]

Isothermal surfaces within the device [Display omitted] • First high-resolution far-infrared study of vinyl acetylene. • Two energetically lowest vibrational fundamentals and their hotbands studied. • Millimeter-wave vibrational satellites reported for the first time. • Global fits of infrared and pure rotational spectra performed. The high resolution vibrational spectrum of vinyl acetylene (C 2 H 3 CCH) has been investigated in the far infrared region from 180 to 360 cm−1 using the Bruker IFS 120 HR spectrometer at Justus-Liebig-Universität, Gießen, Germany. The two energetically lowest vibrational fundamentals ν 13 and ν 18 at 214 cm−1 and 304 cm−1, respectively, were measured at a resolution of 0.0016 cm−1. In addition to the fundamental modes, several hot bands originating from either ν 13 or ν 18 were observed and analyzed. The spectroscopic analysis was supported by high-level quantum-chemical coupled-cluster calculations and also made use of the Automated Spectral Line Assignment Procedure, ASAP, outlined earlier (Martin-Drumel et al., 2015). In addition to the infrared study, so far unpublished millimeter-wave vibrational satellites that were measured in the course of an earlier study of the pure rotational spectrum of vinyl acetylene in its ground vibrational state (Thorwirth and Lichau, 2003) were added to the data set and are reported here for the first time. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phenylpropiolonitrile (C 6 H 5 C 3 N) has been characterized in the gas phase. • Its medium resolution far- and mid-infrared spectrum has been measured for the first time. • Rotational transitions have been recorded in the centimeter- and millimeter-wave range. • Quantum chemistry was used to guide spectroscopic assignments and parameter determina-tion. • We conclude phenylpropiolonitrile is a strong candidate for interstellar detection. The evidence for benzonitrile (C 6 H 5 CN) in the starless cloud core TMC–1 makes high-resolution studies of other aromatic nitriles and their ring-chain derivatives especially timely. One such species is phenylpropiolonitrile (3-phenyl-2-propynenitrile, C 6 H 5 C 3 N), whose spectroscopic characterization is reported here for the first time. The low resolution (0.5 cm−1) vibrational spectrum of C 6 H 5 C 3 N has been recorded at far- and mid-infrared wavelengths (50–3500 cm−1) using a Fourier Transform interferometer, allowing for the assignment of band centers of 14 fundamental vibrational bands. The pure rotational spectrum of the species has been investigated using a chirped-pulse Fourier transform microwave (FTMW) spectrometer (6– 18 GHz), a cavity enhanced FTMW instrument (6–20 GHz), and a millimeter-wave one (75–100 GHz, 141–214 GHz). Through the assignment of more than 6200 lines, accurate ground state spectroscopic constants (rotational, centrifugal distortion up to octics, and nuclear quadrupole hyperfine constants) have been derived from our measurements, with a plausible prediction of the weaker lines through calculations. Interstellar searches for this highly polar species can now be undertaken with confidence since the astronomically most interesting radio lines have either been measured or can be calculated to very high accuracy below 300 GHz. [ABSTRACT FROM AUTHOR]