Phosphorus belongs to the group of the so-called "main biogenic elements", which includes the most abundant elements in living systems. Accordingly, when seeking to better understand the evolution of the universe -with a keen eye on abiogenesis- phosphorus and its compounds cannot be overlooked. However, the chemical evolution of such element in the interstellar medium (ISM) is still far from an accurate characterization.
To provide a contribution in this direction, a recent work investigated the reactivity beetween the CP radical (X²Σ⁺) and methanimine (), both detected in the carbon-rich circumstellar shell IRC+10216. This type of reaction is particularly promising because it fits into a peculiar reactivity of methanimine with different radicals, among which we find the isoelectronic CCH and CN radicals, the reactions with these latter being very well characterized. This supports the idea of a general mechanism for the formation of complex imines in the interstellar clouds.
An accurate investigation of the reactive + CP potential energy surface (PES) revealed the presence of submerged formation pathways for three main reaction products, namely E- and Z-2-phosphanylidyneethan-1-imine (HNCHCP) and N-(phosphaneylidynemethyl)methanimine ().
Despite the proof of concept of their feasible formation in gas phase from an energetic point of view, the laboratory synthesis of species like HNCHCP and is particularly complex. This could hamper the identification of their rotational transitions required in view of predicting and confirming their presence in the ISM.
In order to provide a useful support to experimental measurements, computed spectra represent a mandatory starting point. This talk will delve into the accurate spectroscopic characterization of these latter species with a methodology at the state of the art, which is able to predict rotational transitions with accuracy better than 0.2%.

Pure rotational spectra of Sc¹³C₂ (~X²A₁) and Sc¹²C¹³C (~X²A^′) have been obtained using Fourier Transform microwave/millimeter-wave methods. These molecules were synthesized from the combination of scandium vapor, produce via laser ablation, with mixtures of ¹³CH₄ or ¹³CH₄/¹²CH₄, diluted in argon. The four lowest a-type rotational transitions were observed for both species in the frequency range of 14 – 61 GHz. Each exhibit hyperfine splittings due to the nuclear spins of ¹³C (I = 1/2) and/or Sc (I = 7/2). Rotational, spin-rotation, and hyperfine parameters have been determined for these isotopologues, and a refined structure for ScC₂ established. In addition, a quartic force field was calculated for ScC₂ and its isotopologues using a highly accurate coupled cluster-based composite method, incorporating complete basis set extrapolation, scalar relativistic corrections, outer core and inner core electron correlation, and higher-order valence correlation effects. The ratio of experimental to theoretical (B+C) values is 1.005 for all calculated isotopologues, yielding a promising route towards predictive gas phase rotational spectroscopy for new metal-carbon bearing radicals.

The role of iron containing molecular species in the interstellar medium is not fully understood. Iron monoxide was tentatively detected toward Sagittarius B2.C.M. Walmsley et al., Astrophys. J., 566:L109-L112, (2002).n the laboratory the isotopologues ⁵⁶FeO and ⁵⁴FeO were rotationally measured in all five spin states in their X⁵∆_i ground state by Allen et al.M.D. Allen et al., Chem. Phys. Lett., 257, 130-136, (1996).e present laboratory measurements of rotational lines of the rare isotopologues ⁵⁷FeO, ⁵⁸FeO, and ⁵⁶Fe¹⁸O, including the hyperfine structure splitting due to the nuclear spin I=1/2 of ⁵⁷Fe.B. Waßmuth et al., Mol. Phys., 118, 19-20, (2020).e performed a mass independent analysisA.A. Breier et al., J. Mol. Spectrosc., 355, 46-58, (2019).ith the new isotopic data and data from the literature. This enables us to predict molecular parameters and line transitions of the radioactive isotopologue ⁶⁰FeO. Kami\'nski et al. detected the radioactive molecule ²⁶AlF in the merger CK Vulpeculae by means of rotational spectroscopy T. Kami\'nski et al., Nature Astronomy, 2, 778-783, (2018). This is a powerful novel approach to use molecular transition to search for iron and its isotopes. Iron monoxide is a well suited candidate for a astronomical search for ⁶⁰Fe.

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C.M. Walmsley et al., Astrophys. J., 566:L109-L112, (2002).I M.D. Allen et al., Chem. Phys. Lett., 257, 130-136, (1996).W B. Waßmuth et al., Mol. Phys., 118, 19-20, (2020).W A.A. Breier et al., J. Mol. Spectrosc., 355, 46-58, (2019).w T. Kami\'nski et al., Nature Astronomy, 2, 778-783, (2018)..

INO or Nitrosyl iodide is the simplest form among the family of INOx (x=1 to 3), which may be viewed as important temporary reservoir species for iodine and nitrogen oxides. Since the corresponding chlorine and bromine species have already been well characterized by microwave and millimeter-wave spectroscopy, spectroscopic information of the iodine compounds is very limited. We have successfully measured submillimeter-wave spectrum of INO in 2016, without resolving any hyperfine splitting due to iodine and nitrogen nuclei.S. Bailleux, D. Duflot, S. Aiba, S. Nakahama and H. Ozeki, hem. Phys. Lett. 650, 73-75 (2016)ompletion of this task is mandatory for full understanding of the molecule. We have observed millimeter-wave spectra of INO at millimeter-wave region. Hyperfine splitting were observed at the frequency of around 150 GHz. The electric quadrupole coupling constants for iodine nucleus was determined for the first time. S. Bailleux, D. Duflot, S. Aiba, S. Nakahama and H. Ozeki, hem. Phys. Lett. 650, 73-75 (2016)C

Chlorine nitrate (ClONO₂) is a very important atmospheric "reservoir" of ClO and NO₂, destroying stratospheric ozone through catalytic cyclesP. J. Crutzen, Quart. J. Royal Met. Soc. 96, 320 (1970); M. J. Molina and F. S. Rowland, Nature 249, 810 (1974). It was detected for the first time by infrared (IR) spectroscopyD. G. Murcray et al., Geophys. Res. Lett. 6, 857 (1979). a detection confirmed and extended by the MIPASH. Fischer et al., Atmos. Chem. Phys. 8, 2151 (2008).nd the ATMOS satellite experimentsR. Zander et al., Geophys. Res. Lett. 13, 757 (1986). Many high-resolution microwave and mid-IR spectroscopy studies of ClONO₂ have been publishedJ. Orphal, M. Birk, G. Wagner, and J.-M. Flaud, Chem. Phys. Lett. 690, 82 (2017). However, ClONO₂ presents 4 fundamentals in the far-IR region below 600 cm⁻¹, with the lowest one corresponding to the torsional mode ν₉ around 83.3 μm. This band has been observed at low resolutionJ. W. Fleming, Infrared Phys. 18, 791 (1978); K. V. Chance and W. A. Traub, J. Mol. Spectrosc. 95, 306 (1982).ut without precise determination of the band center. More recently, the analysis of the mid-IR ν₈ and ν₈ + ν₉ band spectral regions of ³⁵ClONO₂ allowed the indirect but accurate determination of the ν₉ band centerJ.-M. Flaud, W. J. Lafferty, J. Orphal, M. Birk, and G. Wagner, Mol. Phys. 101, 1527 (2003). In this work, the 83.3 μm region of ClONO₂ has been recorded at high resolution (0.001 cm⁻¹) using a Fourier transform spectrometer and the SOLEIL synchrotron light source. The spectrum corresponds to the absorption of the torsional mode, ν₉ around 123 cm⁻¹and a series of nν₉-(n-1)ν₉ hot bands. In this talk, the analysis of the ν₉ bands of ³⁵ClONO₂ and ³⁷ClONO₂ and 2ν₉-ν₉ band of ³⁵ClONO₂ will be presented. In turn, this will enable an analysis of the hot bands involving low energy levels in the mid-IR region where ClONO₂ is detected and modelled.

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Footnotes:

P. J. Crutzen, Quart. J. Royal Met. Soc. 96, 320 (1970); M. J. Molina and F. S. Rowland, Nature 249, 810 (1974).. D. G. Murcray et al., Geophys. Res. Lett. 6, 857 (1979)., H. Fischer et al., Atmos. Chem. Phys. 8, 2151 (2008).a R. Zander et al., Geophys. Res. Lett. 13, 757 (1986).. J. Orphal, M. Birk, G. Wagner, and J.-M. Flaud, Chem. Phys. Lett. 690, 82 (2017).. J. W. Fleming, Infrared Phys. 18, 791 (1978); K. V. Chance and W. A. Traub, J. Mol. Spectrosc. 95, 306 (1982).b J.-M. Flaud, W. J. Lafferty, J. Orphal, M. Birk, and G. Wagner, Mol. Phys. 101, 1527 (2003)..

r0pt Figure Trioxane, (H₂CO)₃, is a symmetric top that belongs to the C_3v symmetry group. The molecule owns 20 fundamental modes that are dispatched as 7 symmetric vibrations of type A1, 3 vibrations of type A2 and 10 doubly degenerate vibrations of type E. Infrared spectra of trioxane have been recorded in the 50-650 cm⁻¹ range using a high resolution Bruker IFS 125 interferometer located at the AILES beamline of the SOLEIL synchrotron facility. Owing to its higher brilliance in the far-infrared region, the SOLEIL synchrotron radiation was used to improve the signal-to-noise ratio of the spectrum at the maximal resolution of 0.001 cm⁻¹. We present here a detailed analysis and modeling of intense OCO deformation ν₇ and ν₁₉ modes as well as weaker CH₂ torsion ν₂₀ mode and its first overtone 2ν₂₀. Thanks to the formalism and programs developed in Dijon, we could determine accurately the effective Hamiltonian parameters for these 3 modes.

In the vicinity of evolved stars cosmic dust forms via nucleation processes. Many of the initial steps of nucleation are not well understood but the investigation of small di- and triatomic molecules at radio or infrared wavelengths in these stellar environments can help elucidating the dust formation process. Especially molecules made of refractory material that condense already at temperatures above thousand Kelvin, like aluminum, are thought to act as seed molecules for dust grains. In this work the gas phase spectrum of the symmetric linear dialuminum monoxide Al-O-Al is investigated in our laboratory. Because Al₂O has no permanent electric dipole moment it can not be detected at radio wavelengths but it has a unique infrared ro-vibrational spectrum around 10 μm. We recorded the ro-vibrational absorption spectrum of Al₂O by using a frequency modulated quantum cascade laser in combination with Herriott-type multipass optics. The molecules were produced and rotationally cooled down to around 120 K by laser ablating an aluminum rod and purging the resulting ablation plume with a N₂O/He buffer gas mixture that subsequently underwent an adiabatic expansion into a vacuum chamber. The spectra reveal a line intensity alteration due to the spin-statistical weight induced by two identical spin 5/2 ²⁷Al atoms. The fundamental ν₃= 1-0 as well as five hot band transitions could be observed. Highly precise molecular constants could be determined and a l-type resonance was analyzed. The here presented transition frequencies will allow for astrophysical searches of this molecule in space.

Methane is the first organic molecule detected in hot-Jupiter exoplanets [1] and the observed spectra carry information about the atmospheric conditions, the photochemistry, and planetary formation. To extract this information, we need accurate theoretical models of the spectra verified by high-precision laboratory measurements. However, the energy level structure of highly excited CH₄ is poorly understood; there exist limited line-by-line assignments of laboratory spectra above the Icosad polyad ( 6,000 cm⁻¹). We performed double-resonance spectroscopy using a 3.3 μm continuous wave pump and 1.67 μm frequency comb probe to measure sub-Doppler transitions in the 3ν₃ ← ν₃ range (up to 9000 cm⁻¹) [2-3]. We detected 36 (J’=0-2) transitions with 1.7 MHz frequency accuracy, limited by the stability of the pump. We assigned the transitions using the intensity ratios measured with parallel and perpendicular pump-probe polarizations, and by comparison of transition frequencies and intensities to predictions from the TheoReTS database [4]. Recently, we implemented an enhancement cavity for the comb probe and improved the absorption sensitivity by two orders of magnitude, allowing detection of a wider range of transitions with better signal-to-noise ratio. Our work is the first measurement of sub-Doppler molecular response using a frequency comb and the first verification of the accuracy of the theoretical prediction that start from highly vibrationally excited methane states. [1] M. R. Swain, G. Vasisht, and G. Tinetti, Nature 452, 329 (2008). [2] A. Foltynowicz et al., Phys. Rev. Lett. 126, 063001 (2021). [3] A. Foltynowicz et al., Phys. Rev. A 103, 022810 (2021) [4] M. Rey, A. V. Nikitin, Y. L. Babikov, and V. G. Tyuterev, J. Mol. Spectrosc. 327, 138 (2016).

Nitryl chloride (ClNO₂) is of atmospheric interest, since it is produced by heterogeneous reactions, in the marine troposphere, between NaCl sea-salt aerosols and gaseous N₂O₅B. J. Finlayson-Pitts et al., Nature 337, 241 (1989); W. Behnke et al., J. Aerosol Sci. 24, 115 (1993); H. D. Osthoff et al., Nat. Geosci. 1, 324 (2008). in the polluted continental airL. H. Mielke et al., Environ. Sci. Technol. 45, 8889 (2011); G. J. Phillips et al., Geophys. Res. Lett. 39, L10811 (2012). and possibly also on polar stratospheric clouds, between N₂O₅ and solid HClM. A. Tolbert, M. J. Rossi, and D. M. Golden, Science 240, 1018 (1988); M. T. Leu, Geophys. Res. Lett. 15, 851 (1988). Many high-resolution spectroscopic studies of ClNO₂ in the microwave and mid-infrared regions are availableJ.-M. Flaud, A. Anantharajah, F. Kwabia Tchana et al., JQSRT 224, 217 (2019). However, ClNO₂ presents two fundamentals in the far-infrared region below 600 cm⁻¹, with the lowest one corresponding to the Cl-N stretching mode, ν₃ around 370 cm⁻¹. A new investigation of the ν₃ bands of ³⁵ClNO₂ and ³⁷ClNO₂ has been performed using a high resolution (0.00102 cm⁻¹) Fourier transform spectrum recorded at SOLEIL with highly improved experimental conditions as compared to a previous studyJ. Orphal, M. Morillon-Chapey, S. Klee, G. C. Mellau, and M. Winnewisser, J. Mol. Spectrosc. 109, 101 (1998). leading to a well resolved spectrum. As a consequence, significantly better results than previously were obtained. The line assignments were pursued up to higher J and K_a quantum number values, J = 83 and K_a = 44. For both isotopomers, a total of 6331 transitions were reproduced with a root-mean-square deviation of 2×10⁻⁴ cm⁻¹using a Watson-type A-reduced Hamiltonian. Improved band centers, rotational and centrifugal distortion constants for the ν₃ fundamental bands of ³⁵ClNO₂ and ³⁷ClNO₂ have been determined. The synthetic line list obtained in this study will be interesting for future measurements of ClNO₂ in the atmosphere, e.g. using the new satellite mission FORUM (ESA) covering the 150-1400 cm⁻¹spectral region.

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Footnotes:

B. J. Finlayson-Pitts et al., Nature 337, 241 (1989); W. Behnke et al., J. Aerosol Sci. 24, 115 (1993); H. D. Osthoff et al., Nat. Geosci. 1, 324 (2008)., L. H. Mielke et al., Environ. Sci. Technol. 45, 8889 (2011); G. J. Phillips et al., Geophys. Res. Lett. 39, L10811 (2012)., M. A. Tolbert, M. J. Rossi, and D. M. Golden, Science 240, 1018 (1988); M. T. Leu, Geophys. Res. Lett. 15, 851 (1988).. J.-M. Flaud, A. Anantharajah, F. Kwabia Tchana et al., JQSRT 224, 217 (2019).. J. Orphal, M. Morillon-Chapey, S. Klee, G. C. Mellau, and M. Winnewisser, J. Mol. Spectrosc. 109, 101 (1998).,

r0pt Figure   The study and analysis of heavy spherical-top molecules is often not straightforward. The presence of hot bands and of many isotopologues can lead to a high line congestion very difficult for assignment. In this work, using a low-order model we have derived very simple isotopic relations in order to determine initial parameters of the analysis. We also show that an identical approach can be used for XY₄ and XY₆ molecules and all these results are illustrated by the comparison of numerical computations and experiments for different molecules: CH₄, GeH₄, RuO₄ (as shown in the figure on the right) and SF₆.   Reference: M. Loëte, C. Richard and V. Boudon, J. Mol . Struct. 1206, 127729 (2020).

Three bands of tungsten sulfide, WS, in the 14,900 - 16,100 cm⁻¹ region have have been recorded in high resolution using Intracavity Laser Spectroscopy integrated with Fourier Transform detection (ILS-FTS). WS was formed in the plasma discharge resulting from a 0.05 A – 0.15 A DC current applied to a tungsten-lined copper hollow cathode within the resonator cavity of a dye laser using gas flows of Ar, CS₂, and H₂ at a pressure of approximately 1 torr. Based on isotopologue shifts, the observed WS bands are assigned as the (0,0), (1,0), and (2,0) bands of a new [15.05] Ω=0⁺ – X ³Σ(0⁺) electronic transition, with bandheads near 15,050, 15,575, and 16,094 cm⁻¹, respectively. The observed line positions were rotationally analyzed using PGOPHER, and spectroscopic constants are compared to a previous computational work [L.F. Tsang et al., J. Mol. Spec. 2019 (359), 31-36]. The results of the analysis will be presented.

Vibrational levels of the A²Σ⁺ state of SH (v^′ = 0-7) and SD (v^′ = 0-8) radical are investigated via photodissociation using high-n Rydberg atom time-of-flight technique. By measuring the H-atom product translational energy distributions, contributions from overlapping transitions can be separated, and the H/D-atom photofragment yield (PFY) spectra are obtained across various SH/SD A²Σ⁺← X²Π rovibrational bands. The upper A²Σ⁺ state vibrational levels v^′ = 5-7 of SH and v^′ = 3-8 of SD are observed for the first time. Analysis of the PFY spectra using the simulation program PGOPHERWestern, J. Quant. Spectrosc. Radiat. Transfer, 186, 221 (2016)ives vibrational origins along with rovibrational linewidths of the A²Σ⁺ state of SH/SD. The fitted linewidths in the PFY spectra for SH v^′ = 1-6 and SD v^′ = 2-6 states are broad ( ≥ 1.5 cm⁻¹), demonstrating that those levels undergo rapid predissociation with lifetimes on the order of picosecond. While the lifetime of SD v^′ = 0, N^′= 1 and 2 levels are determined to be 247 ± 30 ns and 168 ± 40 ns from pump-probe time delay measurements, respectively. The experimental lifetimes are in reasonable agreement with the theoretical predictions.

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Footnotes:

Western, J. Quant. Spectrosc. Radiat. Transfer, 186, 221 (2016)g