The very weak absorption spectrum of natural CO₂ near 1.74 μm (5702 - 5879 cm⁻¹) is studied at high sensitivity. The investigated region corresponds to a transparency window of very weak opacity which is of particular interest for Venus. Very weak lines with intensity value as low as 10⁻³⁰ cm/molecule at 296 K are detected by Cavity Ring Down Spectroscopy. On the basis of the predictions of effective Hamiltonian models, 1135 lines of six carbon dioxide isotopologues - ¹²C¹⁶O₂, ¹³C¹⁶O₂, ¹⁶O¹²C¹⁸O, ¹⁶O¹²C¹⁷O, ¹⁶O¹³C¹⁸O and ¹⁶O¹³C¹⁷O - were rovibrationnally assigned to 26 bands. The accurate spectroscopic parameters of 16 bands are determined from standard band-by-band analysis (typical rms deviations of the line positions are 8 ×10⁻⁴ cm⁻¹). These newly observed bands include perturbed bands, weak hot bands and bands of minor isotopologues (in particular ¹⁶O¹²C¹⁸O in natural abundance) and provide critical validation tests for the most recent spectroscopic databases. The comparison to the Carbon Dioxide Spectroscopic Databank (CDSD), HITRAN2016 database and recent ab initio line lists will be presented. Deficiencies are evidenced for some weak perpendicular bands of the HITRAN2016 list and identified as due to inaccurate CDSD intensities which were preferred to ab initio intensities. New results based on ¹⁸O enriched CO₂ spectra will also be detailed.

Germane (GeH₄) is present in the atmospheres of the giant planets Jupiter and Saturn. The ongoing NASA mission Juno has renewed interest in its spectroscopy. The accurate modeling of which is essential for the retrieval of other tropospheric species. We present here the first complete analysis and modeling of line positions and intensities in the strongly absorbing ν₁/ν₃ stretching dyad region near 2100 cm⁻¹, for all five germane isotopologues in natural abundanceV. Boudon, T. Grigoryan, F. Philipot, C. Richard, F. Kwabia Tchana, L. Manceron, A. Rizopoulos, J. Vander Auwera and T. Encrenaz, J. Quant. Spectrosc. Radiat. Transfer 205, 174-183 (2018) New infrared spectra were recorded, absolute intensities were extracted through a careful procedure and modeled thanks to the formalism and programs developed in Dijon. A database of calculated germane lines, GeCaSDa, is available online through the Virtual Atomic and Molecular Data Centre (VAMDC) portal (http://portal.vamdc.org) and at http://vamdc.icb.cnrs.fr/PHP/gecasda.php. GeH₄ will integrate the HITRAN database as molecule number 50.

---

Footnotes:

V. Boudon, T. Grigoryan, F. Philipot, C. Richard, F. Kwabia Tchana, L. Manceron, A. Rizopoulos, J. Vander Auwera and T. Encrenaz, J. Quant. Spectrosc. Radiat. Transfer 205, 174-183 (2018).

Because of their curious electronic properties, carbon-sulfide chains possess peculiar molecular structures and chemical reactivity. In this talk, we present the spectroscopic characterization of ethynethiol (HCCSH) - an isomer of thioketene (H₂CCS) and thiirene (c-H₂C₂S) - and its isotopologues using Fourier-transform microwave cavity and millimeter-wave absorption spectroscopies. HCCSH is produced in an electrical discharge of HCCH and H₂S. In our cavity spectrometer (10 - 40 GHz), the J=1−0, 2−1, 3−2 a-type transitions have been observed. HCC³⁴SH was detected in natural abundance while the deuterated isotologues required HCCD and D₂S for DCCSH and HCCSD respectively. Based on ab initio predictions, the fundamental b-type transitions were also measured using double resonance (150 - 300 GHz), allowing the A constant to be determined approximately and guiding subsequent surveys into the millimeter-wave (280 - 655 GHz). Based on the information derived from the isotopologues, we will also discuss the molecular structure and inferred formation chemistry, in addition to its relative abundance to thioketene.

The millimeter/submillimeter spectrum of F₂SO (~X¹A′) has been measured using direct absorption techniques in the frequency range 271 – 508 GHz. Thionyl fluoride was created in the process of searching for a number of metal-containing fluoride molecules. This species was serendipitously produced from SF₆ as the fluorine source with residual water in the presence of a DC discharge. Multiple rotational transitions in the range J = 16 to J = 30 were recorded, each consisting of a c-type asymmetric top pattern, due to the large dipole moment along the ^c molecular axis μ_c = 1.62 D. The data were analyzed using an asymmetric top Hamiltonian and rotational and centrifugal distortion constants were established. This work considerably expands the spectroscopic characterization of F₂SO. Previous microwave data consisted of measurements below 77 GHz.

The rotational spectra of a series of 1:1 adducts of water-fluoropyridines have been investigated by using pulsed jet Fourier transform microwave spectroscopy. Depending on the fluorination sites, the hydrogen bond topologies are quite different from each other. The water links with the N n-obital of 2,3-difluoropyridine and 2,6-difluoropyridine, respectively. through an O-H...N bond. In addition, one weak C-H...O bond might be contributable to the stabilization of the complex 2,3-difluoropyridine-water, while an O-H...F bond plausibly formed in the complex 2,6-difluoropyridine-water in which water acts as a double proton donor. Additional fluorination of the third site of 2,6-difluoropyridine creates a new active site ready to interact with water: the isomer stabilized by one C-H...O and one O-H...F hydrogen bond is proved by the experimental evidences to be the global minimum. This hydrogen topology is quite different from the all former rotational studied complexes involving pyridine and fluoropyridines.

We have found that the observed average structures of haloethylene-protic acid heterodimers result from an interplay between favorable electrostatic interactions and steric effects. For vinyl fluoride and 1,1-difluoroethylene complexes, steric effects predominate and the acid binds across the double bond ("top"), while for trifluoroethylene, favorable electrostatics forces the complexes to adopt a sterically strained structure with the acid at one end of the olefin ("side"). A relaxation of steric requirements for binding with a chlorine atom leads to different geometries being observed for each of the vinyl chloride complexes with hydrogen fluoride, hydrogen chloride, and acetylene. The side binding motif to chlorine persists in (Z)-1-chloro-2-fluoroethylene–acetylene despite the presence of the more electronegative fluorine atom. For 2-chloro-1,1-difluoroethylene ethylene–acetylene, the acetylene is presented with the option of top binding to fluorine versus side binding to chlorine, whereas with cis-1,2-difluoroethylene, the only option is side binding to fluorine. The structures of these two complexes are compared to reveal the balance between electrostatics and sterics.

Our systematic study of the structures of heterodimers of haloethylenes with protic acids has provided a wealth of information, along with a few surprises, regarding the sometimes cooperative and sometimes competing effects of electrostatic, steric, and dispersion forces that contribute to the binding of these species. We seek to apply this knowledge to larger systems with a wider variety of possible interactions and binding sites via the addition of a trifluoromethyl moiety to the olefin to form halopropenes. The microwave spectrum of the complex formed between 2,3,3,3-tetrafluoropropene, which can be considered a trifluoromethyl analogue of vinyl fluoride, and hydrogen chloride is obtained and analyzed to determine the molecular structure of this species.

Glutamine is α-amino acid that is used in the biosynthesis of proteins. The large flexibility of the molecule has several potential conformational candidates. Among them, the three most stable isomers have been characterized both using a laser ablation chirped pulse Fourier-transform microwave spectrometer (LA-CP-FTMW) and a laser ablation molecular-beam Fourier-transform microwave spectrometer (LA-MB-FTMW).S. Mata, I. Peña, C. Cabezas, J. C. López and J. L. Alonso, J. Mol. Spectrosc., 2012, 280, 91–96.^,J. L. Alonso and J. C. López, in Gas−Phase IR Spectroscopy and Structure of Biological Molecules, eds. A. M. Rijs and J. Oomens, Topics in., 2015, vol. 364, pp. 335–402.wo of the conformers can be determined using the spectroscopic constants provided by the theoretical methods. On the other hand, the third conformer is not reproduced by conventional theoretical methods and one should use some tricks to characterize the conformer’s structure. In addition, even the slightest different prediction in the site position of the nitrogen atoms makes the conformer’s spectroscopic characterization very challenging because the nuclear quadrupole coupling interactions depend critically on the electronic environment, position and orientation of the ^14 J. L. Alonso and J. C. López, in Gas-Phase IR Spectroscopy and Structure of Biological Molecules, eds. A. M. Rijs and J. Oomens, Topics in., 2015, vol. 364, pp. 335–402.T

r0pt Figure The dimers of thenyl alcohol (TA₂) and furfuryl alcohol (FA₂), and the monohydrates of both alcohols (TA···H₂O, FA···H₂O) and their corresponding mercaptans (TM···H₂O, FM···H₂O) were generated in a supersonic jet expansion and probed using both chirped-pulse and cavity Fourier transform microwave spectroscopy. The experimental results, supported by ab initio molecular orbital calculations, allow comparing the conformational preferences and the role of the sulfur and oxygen atoms in the O-H···O/O-H···S/S-H···O hydrogen bonds (HBs) stabilizing the dimers. In the furfuryl monohydrates (FA···H₂O, FM···H₂O) water behaves as a proton donor to the ring oxygen, in competence with a second HB to the alcohol or thiol side chainM. Juanes, A. Lesarri, R. Pinacho, E. Charro, J. E. Rubio, L. Enriquez, M. Jaraiz, Chem. Eur. J., 2018, 24, 1–9, in press Different behavior was observed when the ring oxygen is replaced by sulfur atom in the thenyl monohydrates (TA··· H₂O and TM···H₂O) as the water molecule is binding to the side chain and the π electronic cloud of the ring. The water motion in both thenyl dimers is detected by tunneling splittings of the rotational transitions, denoting a weaker binding compared to the furfuryl compounds. The alcohol dimers (TA)₂ and (FA)₂ again reveal the different HB strengths in the furfuryl and thenyl groups. The alcohol dimer forms a network of two consecutive O-H···O hydrogen bonds involving the oxygen ring, while in the thenyl dimer the alcohol group prefers binding to the π cloud than to the sulfur atom in the ring. Spectroscopic, structural and computational data will be reported.

---

Footnotes:

M. Juanes, A. Lesarri, R. Pinacho, E. Charro, J. E. Rubio, L. Enriquez, M. Jaraiz, Chem. Eur. J., 2018, 24, 1–9, in press.

Rotational spectra of 1,1-difluorosilacyclopent-3-ene, silacyclopent-3-ene, 1-(chloromethyl)-1-fluoro-silacyclopentane, 1,1-difluorosilacyclopentane, and 1,1-difluorosilacylopent-2-ene were observed in the 6 to 18 GHz range of the electromagnetic spectrum. The molecular structure for the parent and various isotopically substituted species were obtained from their respective spectra. The differences in structure between these similar molecules will be presented, showing how different functional groups and bond locations affect the overall structure and behavior of each system (ring puckering effects, etc.). Comparisons to similar known cyclopentane and silacyclopentane species will be presented.