THE JET-COOLED HIGH-RESOLUTION IR SPECTRUM OF FORMIC ACID CYCLIC DIMER

As the simplest carboxylic acid, formic acid (FA) is an excellent model molecule to investigate the general properties of carboxylic acids. FA is also an atmospherically and astrophysically relevant molecule. It is well known that its dimeric form is predominant in the gas phase at temperatures below 423 K.footnote{T. Miyazawa and K. S. Pitzer, J. Am. Chem. Soc. 81, 74, 1959} The cyclic conformation of the dimer (FACD) is an elementary system to be understood for the concerted hydrogen transfer through equivalent hydrogen bonds, an essential process within biomolecules. The IR range is a crucial spectral region, particularly the far-IR, as it gives a direct access to the intermolecular vibrational modes involved in this process. Moreover, due to its centrosymmetric conformation, the FACD exhibits no pure rotation spectrum and, due to spectral line congestion and Doppler broadening, IR bands cannot be rotationally resolved at room temperature.footnote{R. Georges, M. Freytes, D. Hurtmans, I. Kleiner, J. Vander Auwera, M. Herman, Chem. Phys. 305, 187, 2004} So far, only parts of the $nu_{5}$-GS band (C-O stretch) have been observed under jet-cooled conditions using laser techniques.footnote{M. Ortlieb and M. Havenith, J. Phys. Chem. A 111, 7355, 2007; K. G. Goroya, Y. Zhu, P. Sun and C. Duan, J. Chem. Phys. 140, 164311, 2014} par_x000d_ We present here six rotationally resolved IR bands of FACD recorded under jet-cooled conditions using the Jet-AILES apparatus and the QCL spectrometer at MONARIS, including the far-IR $nu_{24}$-GS band (intermolecular in-plane bending). Splitting due to vibration-rotation-tunneling motions are clearly observed. A full spectral analysis is in progress starting from the GS constants obtained by Goroya et al. and with the support of electronic structure calculations.footnote{This work is supported by the CaPPA project (Chemical and Physical Properties of the Atmosphere) ANR-11-LABX-0005-01

Conformational Landscape of Oxygen-Containing Naphthalene Derivatives

Polycyclic aromatic compounds (PACs) constitute an important class of molecules found in various environments and are considered important pollutants of the Earth's atmosphere. In particular, functionalization of PACs modify the ring aromaticity, which greatly influences the chemical reactivity of these species. In this work we studied several oxygen-containing PACs, relevant to atmospheric chemistry. We investigated the conformational landscape of four naphthalene-derivative molecules -- namely ,1- and 2-hydroxynaphthalene and 1- and 2-naphthaldehyde -- by means of rotational and vibrational spectroscopy supported by quantum chemical calculations. For 1-hydroxynaphthalene and 1-naphthaldehyde, intramolecular hydrogen bonding and steric effects drive the conformational preferences while for 2-hydroxynaphthalene and 2-naphthaldehyde, the charge distributions allow us to understand the conformational landscape. This work not only demonstrates how the localization of the substitution group in the ring influences the conformational relative energies and but also constitutes a step toward a better understanding of the different chemical reactivity of such functionalized PACs

The far-infrared spectrum of azulene and isoquinoline and supporting anharmonic density functional theory calculations to high resolution spectroscopy of polycyclic aromatic hydrocarbons and derivatives

International audienceIn the laboratory, the acquisition and analysis of the rotationally resolved spectra of large molecular systems remain challenging. We report in this paper the rotational analysis of the ν30-GS band of azulene and the ν41-GS band of isoquinoline recorded with synchrotron-based Fourier transform absorption spectroscopy in the far-IR. As a support to rotational analyses, we employed a method based on standard density functional theory calculations performed at the anharmonic level which accurately reproduced the rotational constants of 28 vibrational states of 16 Polycyclic Aromatic Hydrocarbons (PAHs) and aza-derivatives. This method appears as an invaluable support for the spectral assignment of the very congested rotational structures of the infrared bands of PAH species and should be very helpful in the active search of these molecules in space through their pure rotational or rovibrational spectra

Dynamique vibrationnelle des complexes à liaison hydrogène (CH2)2S - HF et (CH2)2S - DF étudiée par spectroscopie infrarouge à transformée de Fourier et calculs ab initio

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Coupled Anharmonic Vibrational Dynamics of the Hydrogen Bond in Binary Complexes: Editorial and Review

We report anharmonic vibrational analyses of the coupling between the red-shifted high frequency HFstretching vibrations and low frequency intermolecular modes in the hydrogen-bonded complexes thiirane-HF and H2 O-HF. The important non-diagonal anharmonicities found in high-level ab initio calculations are consistent with recent experimental results. The physical origin of the coupling mechanism implies that a physically correct treatment of hydrogen-bond induced vibrational red shifts requires a vibrational treatment far beyond the customary one-dimensional approach combined with large basis set electronic structure calculations

Structural and dynamic properties of a hydrogen bond from the study of the CH3Cl-HCl complex and isotopic species.

International audienceThe microwave (4-20 GHz range) and infrared (HCl and DCl stretch ranges) spectra of six isotopic species of the CH3Cl-HCl hydrogen bond complex have been recorded for the first time and analyzed with the support of high level ab initio calculations (MP2 and CCSD(T) levels). Accurate molecular parameters, including rotational, quartic centrifugal distortion, and nuclear-quadrupole coupling constants, vibrational frequencies, and anharmonic coupling constants, are presented in this paper. These parameters have then been used to estimate the hydrogen bond geometry and confirm the strong coupling between intramolecular and low frequency intermolecular modes. Experimental and theoretical evidence, in agreement with each other, tend to point out a free rotation of the CH3Cl unit in the complex, emphasizing the very peculiar dynamical properties of a hydrogen bond and, consequently, the necessity of taking those effects into account to correctly model the intra- and intermolecular interactions

The hydration of polycyclic aromatic compounds: the case of naphthaldehyde

International audiencePolycyclic aromatic hydrocarbons (PAHs) and their oxygenated products (oxi-PAH) are considered as important pollutants of the Earth’s atmosphere since they are emitted by the combustion of fuels. [1] The study of their intermolecular interactions is essential to understand the formation of their aerosols. In this work, we have studied at molecular level the interactions present in the hydration of the oxi-PAH, α- and β-naphthaldehyde. This study has been performed using a supersonic jet Fourier transform microwave (FTMW) spectrometer in the 4-15 GHz range, with the support of theoretical calculations. Both isolated α- and β-naphthaldehyde species could present two possible structures: cis, the most stable one for α, and trans for β. [2] Our calculations show that there are three low energy monohydrates predicted for each conformer, cis/trans, in an energy range of 1500 cm-1. Experimentally, one conformer has been observed in gas phase for α and two for β, corresponding to the calculated most stable structures. All species are stabilized by intermolecular hydrogen bonds between the water molecule and the aldehyde group of naphthaldehyde: for the α isomer, the oxygen of the aldehyde acts as proton acceptor and the aldehyde hydrogen as proton donor; for the β isomer, the oxygen of the aldehyde acts as proton acceptor and one of the ring hydrogens as a proton donor.[3][1] Karavalakis G. et al. Sci. Tot. Environ., 409, 4, 738, 2011.[2] Goubet M., et al. J. Phys. Chem. A, 124, 4484, 2020.[3] This work is supported by the CaPPA project and by the CPER ClimiBio funded by the French National Research Agency (ANR) through the PIA 11-LABX-0005-01, the I-SITE ULNE/ANR-16-IDEX-0004 ULNE, the Regional Council Hauts-de-France and the European Funds for Regional Economic Development (FEDER)

Jet-cooled and long path cell high resolution infrared spectroscopy of furfural conformers from Fourier transform and QCL measurements

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Large Amplitude Torsions in Nitrotoluene Isomers Studied by Rotational Spectroscopy and Quantum Chemistry Calculations

Rotational spectra of ortho-nitrotoluene (2-NT) and para-nitrotoluene(4-NT) have been recorded at low and room temperatures using a supersonic jet Fourier Transform microwave (MW) spectrometer and a millimeter-wave frequency multiplier chain, respectively. Supported by quantum chemistry calculations,the spectral analysis of pure rotation lines in the vibrational ground state has allowed to characterise the rotational energy, the hyperfine structure due to the 14N nucleus and the internal rotation splittings arising from the methyl group. For 2-NT, an anisotropic internal rotation of coupled CH3 and NO2 torsional motions was identified by quantum chemistry calculations and discussed from the results of the MW analysis. The study of the internal rotation splittings in the spectra of three NT isomers allowed to characterise the internal rotation potentials of the methyl group and to compare them with other mono-substituted toluene derivatives in order to study the isomeric influence on the internal rotation barrier

Far-Infrared Collision-Induced Absorption in CO2 at T = 200 K

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