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We provide compelling experimental and theoretical evidence for the transition state nature of the cyclopropyl cation. Synchrotron photoionization spectroscopy employing coincidence techniques together with a novel simulation based on high accuracyab initiocalculations reveal that the cation is unstableviaits allowed disrotatory ring opening path. The ring strains of the cation and the radical are similar, but both ring opening paths for the rad- ical are forbidden when the full electronic symmetries are considered. These findings are discussed in light of the early predictions by Longuet-Higgins alongside Woodward and Hoff- man; we also propose a simple phase space explanation for the appearance of the cyclopropyl photoionization spectrum. The results of this work allow the refinement of the cyclopropane C−H bond dissociation energy, in addition to the cyclopropyl radical and cation cyclization energies,viathe Active Thermochemical Tables approach.

International audience; We demonstrate for the first time a novel THz photomixing paradigm exploiting ultrabroadband inverse spin Hall emitters. Both narrow band (∼20 Hz) CW emission by beating of two stabilized IR DFB lasers on a Pt/CoFeB/W stack is obtained as well as successful spintronic downconversion of a IR frequency comb to a THz comb with 1GHz spacing.

International audience; Quantum cascade laser-pumped terahertz (THz) gas lasers are at the edge ofrevolutionizing THz science where powerful yet tunable sources have long beenlacking. Maybe one of the last remaining drawbacks to a wider use of theseinstruments lies in the lack of available databases of potentially lasing transitionsfor users. A new figure of merit, the molecular gain factor is proposed, that allowsto discriminate transitions by their lasing potential. Using this factor, catalogs ofTHz laser lines of ammonia, both 14 NH 3 and 15 NH 3 , up to 10 THz are reported.Demonstration of the use of these two catalogs, and of the pertinence of themolecular gain factor, is made by experimentally observing 32 laser lines of14 NH 3 and 5 lines of 15 NH 3 up to 5.5 THz. Prospects to generalize the use of thismolecular gain factor to a wide range of molecules are discussed

International audience; The far-infrared spectrum of HC3N has been recorded at high resolution between 70 and 500 cm 1 using 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 rovibrational 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.

Additional details on the experimental method, data analysis, and a full list of recorded molecular transitions and their parameters.

International audience; The high resolution vibrational spectrum of vinyl acetylene (C2H3CCH) 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 ν13 and ν18 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 ν13 or ν18 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.

A longstanding problem in astrochemistry is the inability of many current models to account for missing sulfur content. Many relatively simple species that may be good candidates to sequester sulfur have not been measured experimentally at the high spectral resolution necessary to enable radioastronomical identification. On the basis of new laboratory data, we report searches for the rotational lines in the microwave, millimeter, and submillimeter regions of the sulfur-containing hydrocarbon HCCSH. This simple species would appear to be a promising candidate for detection in space owing to the large dipole moment along its b-inertial axis, and because the bimolecular reaction between two highly abundant astronomical fragments (CCH and SH radicals) may be rapid. An inspection of multiple line surveys from the centimeter to the far-infrared toward a range of sources from dark clouds to high-mass star-forming regions, however, resulted in nondetections. An analogous search for the lowest-energy isomer, H₂CCS, is presented for comparison, and also resulted in nondetections. Typical upper limits on the abundance of both species relative to hydrogen are 10^(−9)–10^(−10). We thus conclude that neither isomer is a major reservoir of interstellar sulfur in the range of environments studied. Both species may still be viable candidates for detection in other environments or at higher frequencies, providing laboratory frequencies are available.

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.

Rotational lines of the positive molecular ion C_3H^+ and of the neutral C_3H radical in three new vibrationally excited states with ^2Σ symmetry have been detected in a supersonic molecular beam in the centimeter-wave band. The fundamental rotational line of the ion is quite weak, but is observed with similar intensity in a dc discharge through several different hydrocarbon gases when helium is the buffer gas. Under these conditions, the fractional abundance of C_3H^+ relative to C_3H is estimated to be of order 10^(−4), i.e., toward the lower end of the ratio (10^(−3)–10^(−4)) found for protonated ions using the same discharge nozzle. For each new ^2Σ state of the C_3H radical, spectroscopic constants, including those describing hydrogen hyperfine structure, have been determined to high precision. Lines of one ^2Σ state (B = 11271 MHz) are particularly intense in our molecular beam; for this state and a second one (B = 11306 MHz), millimeter-wave transitions have also been observed between 180 and 340 GHz using a long path dc glow absorption spectrometer. On the basis of intensity measurements with this spectrometer, the inferred rotation–vibration constant α, and theoretical calculations, the state with B = 11271 MHz is tentatively assigned to the ν_5 bending mode, predicted to lie ~300 cm^(−1) above ground.