Olivier Pirali

Far-infrared spectroscopy of small polycyclic aromatic hydrocarbons

Both experimental and theoretical spectroscopic studies on small gas phase polycyclic aromatic hydrocarbons in the far-infrared spectral region are reported. The experimental set-up based on thermal emission and Fourier transform far infrared analysis led to the detection of relatively broad vibrational bands, unresolved in rotation, representative of each molecule. Detailed theoretical investigations were performed, including both ab initio calculations and spectral simulations. For the majority of the samples, this study provides the first detection of the vibrational modes associated with the skeleton motions.

The (CH2)2O-H2O hydrogen bonded complex. Ab Initio calculations and Fourier transform infrared spectroscopy from neon matrix and a new supersonic jet experiment coupled to the infrared AILES beamline of synchrotron SOLEIL.

A series of hydrogen bonded complexes involving oxirane and water molecules have been studied. In this paper we report on the vibrational study of the oxirane-water complex (CH(2))(2)O-H(2)O. Neon matrix experiments and ab initio anharmonic vibrational calculations have been performed, providing a consistent set of vibrational frequencies and anharmonic coupling constants. The implementation of a new large flow supersonic jet coupled to the Bruker IFS 125 HR spectrometer at the infrared AILES beamline of the French synchrotron SOLEIL (Jet-AILES) enabled us to record first jet-cooled Fourier transform infrared spectra of oxirane-water complexes at different resolutions down to 0.2 cm(-1). Rovibrational parameters and a lower bound of the predissociation lifetime of 25 ps for the v(OH)(b) = 1 state have been derived from the rovibrational analysis of the ν(OH)(b) band contour recorded at respective rotational temperatures of 12 K (Jet-AILES) and 35 K (LADIR jet).

High resolution spectroscopy of six SOCl2 isotopologues from the microwave to the far-infrared

Despite its potential role as an atmospheric pollutant, thionyl chloride, SOCl2, remains poorly characterized in the gas phase. In this study, the pure rotational and ro-vibrational spectra of six isotopologues of this molecule, all detected in natural abundance, have been extensively studied from the cm-wave band to the far-infrared region by means of three complementary techniques: chirped-pulse Fourier transform microwave spectroscopy, sub-millimeter-wave spectroscopy using frequency multiplier chain, and synchrotron-based far-infrared spectroscopy. Owing to the complex line pattern which results from two nuclei with non-zero spins, new, high-level quantum-chemical calculations of the hyperfine structure played a crucial role in the spectroscopic analysis. From the combined experimental and theoretical work, an accurate semi-experimental equilibrium structure (r(e)(SE)) of SOCl2 has been derived. With the present data, spectroscopy-based methods can now be applied with confidence to detect and monitor this species, either by remote sensing or in situ.

Synchrotron based FT-FIR pure rotational spectroscopy of the NH2 radical in its two lowest vibrational states.

Six Fourier-transform FIR spectra of the NH2 radical have been recorded at high resolution (0.001 cm(-1)) using synchrotron radiation on the AILES beamline at SOLEIL Synchrotron. Three different experimental discharge setups have been used to observe, in absorption, 1009 pure rotational transitions of NH2 in the vibrational ground state (000) and 170 pure rotational transitions within the first excited vibrational state (010). These results constitute a significant extension of the observed quantum numbers for these two states. The spectra permitted several couplings to be resolved (asymmetric coupling, spin-rotation coupling, hyperfine structure) for relatively highly excited energy levels. An effective fit has been realized using both standard Watson-S and -A reductions despite an abnormal centrifugal distortion effect for this light hydride.

Synthesis, High-Resolution Infrared Spectroscopy, and Vibrational Structure of Cubane, C8H8

Carbon-cage molecules have generated a considerable interest from both experimental and theoretical points of view. We recently performed a high-resolution study of adamantane (C10H16), the smallest hydrocarbon cage belonging to the diamandoid family ( Pirali , O. ; et al. J. Chem. Phys. 2012 , 136 , 024310 ). There exist another family of hydrocarbon cages with additional interesting chemical properties: the so-called platonic hydrocarbons that comprise dodecahedrane (C20H20) and cubane (C8H8). Both possess C-C bond angles that deviate from the tetrahedral angle (109.8°) of the sp(3) hybridized form of carbon. This generates a considerable strain in the molecule. We report a new wide-range high-resolution study of the infrared spectrum of cubane. The sample was synthesized in Bari upon decarboxylation of 1,4-cubanedicarboxylic acid thanks to the improved synthesis of literature. Several spectra have been recorded at the AILES beamline of the SOLEIL synchrotron facility. They cover the 600-3200 cm(-1) region. Besides the three infrared-active fundamentals (ν10, ν11, and ν12), we could record many combination bands, all of them displaying a well-resolved octahedral rotational structure. We present here a preliminary analysis of some of the recorded bands, performed thanks the SPVIEW and XTDS software, based on the tensorial formalism developed in the Dijon group. A comparison with ab initio calculations, allowing to identify some combination bands, is also presented.

ANOMALOUS CENTRIFUGAL DISTORTION IN NH2

The NH2 radical spectrum, first observed by Herzberg and Ramsay, a is dominated by a strong Renner-Teller effectb giving rise to two electronic states: the bent X B1 ground state and the quasi-linear A A1 excited state. The NH2 radical has been the subject of numerous high-resolution investigations and its electronic and ro-vibrational transitionsc have been measured. Using synchrotron radiation, new rotational transitions have been recently recorded and a value of the rotational quantum number N as large as 26 could be reached.d In the X B1 ground state, the NH2 radical behaves like a triatomic molecule displaying spin-rotation splittings. Due to the lightness of the molecule, a strong coupling between the overall rotation and the bending mode arises whose effects increase with N and lead to the anomalous centrifugal distortion evidenced in the new measurements. In this talk the Bending-Rotation approache developed to account for the anomalous centrifugal distortion of the water molecule is modified to include spin-rotation coupling and applied to the fitting of high-resolution data pertaining to the ground electronic state of NH2. A preliminary line position analysis of the available data c,d allowed us to account for 1681 transitions with a unitless standard deviation of 1.2. New transitions could also be assigned in the spectrum recorded by Martin-Drumel et al. In the talk, the results obtained with the new theoretical approach will be compared to those retrieved with a Watson-type Hamiltonian and the effects of the vibronic coupling between the ground X B1 and the excited A A1 electronic state will be discussed.

FOURIER TRANSFORM ABSORPTION SPECTROSCOPY OF C3 IN THE ν3 ANTISYMMETRIC STRETCH MODE REGION

The C3 molecule has been detected in a variety of astrophysical objects thanks to the well-known 4050 Å (AΠu– XΣg ) electronic transition as well as the two IR active modes of the electronic ground state: ν2 (∼ 63.42 cm−1) and ν3 (∼ 2040.02 cm−1)b. Previous laboratory data in the ν3 region, obtained using diode laser spectroscopy and the photolysis of allene to produce C3, permitted measurement of the fundamental (0,0,1)Σ–(0,0,0)Σ as well as the hot bands: (0,1,1)Π– (0,1,0)Π; (0,2,1)Σ–(0,2,0)Σ; (0,2,1)∆–(0,2,0)∆ and provided insights on the anharmonicity of the (0,nν2,1) vibrational patternc. We have recorded the absorption spectrum of C3 in the 1800–2100 cm−1 region (at a resolution of 0.003 cm−1) using the Bruker IFS 125 Fourier Transform spectrometer at the AILES beamline of Synchrotron SOLEIL. C3 was produced in a DC discharge of methane heavily diluted in helium. The rovibrational temperature of C3 produced in our discharge is noticeably higher than in Ref. [4], which allowed us to extend measurements to higher J values. More interestingly, we assigned new hot bands involving higher quanta of the ν2 bending states: (0,nν2,1) with n ranging from 0 to 5. Despite the absence of Q branches for these bands, which results in a possible ambiguous J-assignment of P and R lines, the large variety of data considered in this work, in addition to our experimental data and including observations of comet spectra, allows confident assignments.

14NH3 LINE POSITIONS AND INTENSITIES IN THE FAR-INFRARED: COMPARISON OF FT-IR MEASUREMENTS TO EMPIRICAL HAMILTONIAN MODEL PREDICTIONS

KEEYOON SUNG, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; SHANSHAN YU, Molecular Spectroscopy, Jet Propulsion Laboratory, Pasadena, CA, USA; JOHN PEARSON, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; OLIVIER PIRALI, AILES beamline, Synchrotron SOLEIL, Saint Aubin, France; F. KWABIA TCHANA, CNRS, Université Paris Est Créteil et Paris Diderot, LISA, Créteil, Val de Marne, France; LAURENT MANCERON, Beamline AILES, Synchrotron SOLEIL, Saint-Aubin, France.

THE H2O-CH3F COMPLEX: A COMBINED MICROWAVE AND INFRARED SPECTROSCOPIC STUDY SUPPORTED BY STRUCTURE CALCULATIONS

SHARON PRIYA GNANASEKAR, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, India; MANUEL GOUBET, Laboratoire PhLAM, Université de Lille 1, Villeneuve de Ascq, France; ELANGANNAN ARUNAN, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore, India; ROBERT GEORGES, IPR UMR6251, CNRS Université Rennes 1, Rennes, France; PASCALE SOULARD, PIERRE ASSELIN, MONARIS UMR8233, CNRS UNiversité Paris 6 UPMC, Paris, France; T. R. HUET, Laboratoire PhLAM, UMR8523 CNRS Université Lille 1, Villeneuve d’Ascq, France; OLIVIER PIRALI, AILES beamline, Synchrotron SOLEIL, Saint Aubin, France.

FT-IR MEASUREMENTS OF NH3 LINE INTENSITIES IN THE 60 – 550 CM−1 USING SOLEIL/AILES BEAMLINE

KEEYOON SUNG, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; SHANSHAN YU, Molecular Spectroscopy, Jet Propulsion Laboratory, Pasadena, CA, USA; JOHN PEARSON, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; LAURENT MANCERON, Beamline AILES, Synchrotron SOLEIL, Saint-Aubin, France; F. KWABIA TCHANA, LISA, CNRS, Universités Paris Est Créteil et Paris Diderot, Créteil, France; OLIVIER PIRALI, AILES beamline, Synchrotron SOLEIL, Saint Aubin, France.