Search

We report on the first successful rovibrational study of gas phase mononitrotoluene and dinitrotoluene in the TeraHertz/Far-Infrared (THz/FIR) spectral domain. Using the AILES beamline of the synchrotron SOLEIL and a Fourier Transform spectrometer connected to multipass cells, the low-energy vibrational cross-sections of the different isomers of mononitrotoluene have been measured and compared to calculated spectra with the density functional theory including the anharmonic contribution. The active FIR modes of 2,4 and 2,6 dinitrotoluene have been assigned to the vibrational bands measured by Fourier Transform FIR spectroscopy of the gas-phase molecular cloud produced in an evaporating/recondensating system. This study highlights the selectivity of gas phase THz/FIR spectroscopy allowing an unambiguous recognition and discrimination of nitro-aromatic compounds used as explosive taggants., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The far infrared spectrum of cis-methyl formate has been recorded on the AILES beamline of the synchrotron SOLEIL using a Fourier transform infrared spectrometer coupled to a long path cell. The very weak fundamental band associated with the methyl-top torsion mode (ν18) was observed. The frequency analysis was performed using the 'rho axis method', and the microwave and millimeter-wave data from the literature. A precise determination of the band origins (ν18A = 132.4303 cm-1 and ν18E = 131.8445 cm-1) and of the barrier height [V3 = 370.7398 (58) cm-1] have been obtained. The intensity of the ν18 fundamental band was determined to be 3.4 × 10-21 cm-1/(molecule cm-2) at 297 K, equally shared among A-A and E-E transitions, thus leading to a dipole moment component μc(3) equal to 0.0483 D. The results were compared with the ab initio calcula-tions of Senent et al. [Astrophys. J. 627, 567 (2005)]. [ABSTRACT FROM AUTHOR]

Hexamethylenetetramine (HMT), C 6 N 4 H 12 is a spherical top with nine IR-active modes. Because of its relevance for astrophysics, we recorded the absorption spectra in the full range of its fundamental bands. In total, we detected eight fundamental bands and recently published the rotational analysis of the four most intense bands ( ν 19 , ν 20 , ν 21 , ν 22 ) located in the 1000–1500 cm −1 range as a support for astronomical searches (Pirali et al., 2014). While the CH stretch modes are unresolved broad features, in this article we report the analysis of the two remaining fundamental bands exhibiting rotationally resolved structures: ν 23 –GS and ν 24 –GS located at about 820 cm −1 and 670 cm −1 , respectively. [ABSTRACT FROM AUTHOR]

Six Fourier-transform FIR spectraof the NH2radicalhave 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 NH2inthe vibrational ground state (000) and 170 pure rotational transitionswithin the first excited vibrational state (010). These results constitutea significant extension of the observed quantum numbers for thesetwo 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 hasbeen realized using both standard Watson-S and -A reductions despitean abnormal centrifugal distortion effect for this light hydride. [ABSTRACT FROM AUTHOR]

Both emission and absorption techniques have been developed at the AILES beamline of SOLEIL synchrotron to record far infrared (FIR) spectra of transient species. To illustrate the possibilities offered by our absorption set-up, we report in this paper new rotational transitions of the SO radical falling in the spectral range covered by the HIFI spectrometer onboard Herschel. [ABSTRACT FROM AUTHOR]

Context. High-resolution rotational spectroscopy of the imidogen radical has been limited to the 14NH and 14ND isotopologues. Imidogen is an important intermediate in the astronomical synthesis of ammonia. Recently, the 14N/15N isotopic ratio in ammonia has been obtained in cold, dense molecular clouds. Aims. We conducted a laboratory search for rotational transitions of 15NH to investigate in more detail the 14N/15N ratio in the interstellar medium. Methods. 15NH was generated in a positive column discharge in a flowing 15NH3 - He (SOLEIL synchrotron) or 15NH3 -Ar (PhLAM) mixture. High-resolution spectroscopic study of the 15NH isotopologue of imidogen in its ground electronic and vibrational state (X∼ 3Σ -) was carried out in the THz range (up to 225 cm-1) with the AILES beamline of the SOLEIL synchrotron and subsequently with the PhLAM spectrometer (around 942 GHz). The observed fine and hyperfine structures were analysed, yielding an accurate set of rotational, fine, and hyperfine parameters. Results. The reported frequencies and molecular constants are suitable for radioastronomical searches of this key species and for 14N/15N isotopic ratio astronomical determination. [ABSTRACT FROM AUTHOR]

Experimental far-infrared (FIR) spectroscopy of transient species (unstable molecules, free radicals, and ions) has been limited so far in both emission and absorption (mainly by the low probability of spontaneous emission in that spectral range and the low brightness of continuum sources used for absorption measurements, respectively). Nevertheless, the FIR spectral range recently became of high astrophysical relevance thanks to several new observational platforms (HERSCHEL, ALMA...) dedicated to the study of this region suitable for the detection of the emission from cold objects of the interstellar medium. In order to complete the experimental dataset concerning transient species, three discharge experiments dedicated to the recording of high resolution FIR spectra of radicals have been developed at the Advanced Infrared Line Exploited for Spectroscopy (AILES) which extracts the bright FIR synchrotron continuum of the synchrotron facility SOLEIL. These experiments make use of a high resolution (R = 0.001 cm-1) Bruker IFS125 Fourier transform (FT) spectrometer. An emission setup (allowing to record spectra of radicals excited at high rotational and vibrational temperatures) and two absorption setups (exploiting the bright synchrotron source at the highest resolution available on the FT) are alternatively connected to the FT. The advantages and limitations of these techniques are discussed on the basis of the recent results obtained on OH and CH radicals. These results constitute the first FIR spectra of radicals using synchrotron radiation, and the first FIR spectrum of a C-bearing radical using FT-spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: Following our recent study devoted to measurements of intensities of pure rotation lines of methane, room temperature far infrared spectra of methane diluted in nitrogen at five total pressures between 100 and 800hPa have been recorded at the AILES beamline of the SOLEIL synchrotron. One hundred and five N2 broadening coefficients of methane pure rotation lines have been measured in the 83–261cm−1 spectral range using multi-spectrum non-linear least squares fitting of Voigt profiles. Pressure-induced line shifts were not needed to fit the spectra to the noise level and line mixing effects were neglected. One hundred and seventy-six self broadening coefficients have also been measured in the 59–288cm−1 spectral range using the pure methane spectra recorded in our previous work. The measured N2 broadening coefficients were compared to semi-classical calculations. [Copyright &y& Elsevier]

Context. High-resolution rotational spectroscopy of the imidogen radical has been limited to the 14NH and 14ND isotopologues. Imidogen is an important intermediate in the astronomical synthesis of ammonia. Recently, the 14N/15N isotopic ratio in ammonia has been obtained in cold, dense molecular clouds. Aims. We conducted a laboratory search for rotational transitions of 15NH to investigate in more detail the 14N/15N ratio in the interstellar medium. Methods. 15NH was generated in a positive column discharge in a flowing 15NH3 - He (SOLEIL synchrotron) or 15NH3 -Ar (PhLAM) mixture. High-resolution spectroscopic study of the 15NH isotopologue of imidogen in its ground electronic and vibrational state (X∼ 3Σ -) was carried out in the THz range (up to 225 cm-1) with the AILES beamline of the SOLEIL synchrotron and subsequently with the PhLAM spectrometer (around 942 GHz). The observed fine and hyperfine structures were analysed, yielding an accurate set of rotational, fine, and hyperfine parameters. Results. The reported frequencies and molecular constants are suitable for radioastronomical searches of this key species and for 14N/15N isotopic ratio astronomical determination. [ABSTRACT FROM AUTHOR]

Abstract: The first far-infrared high resolution absorption measurement of the cis-methyl nitrite molecule has been recorded in the range 15–400cm−1 using the synchrotron AILES beamline radiation at SOLEIL with a resolution of 0.0011cm−1. First assignments for the pure rotational transitions (15–65cm−1) belonging to the ground νt (=ν 15)=0 and first νt =1 excited torsional state are based on measurements from previous studies performed in the 13–40GHz spectral range, as well as on new millimeter-wave measurements performed at Lille in the spectral range 75–465GHz. A few measurements and remeasurements in the 1.8–13GHz were also performed using the chirped FT-MW spectrometer located in North Texas. The pure rotational transitions in the far-infrared and in the microwave spectral range belonging to the two first torsional states have been globally fitted using the RAM (“Rho Axis Method”) dealing with the rotation–torsion Hamiltonian and implemented in the BELGI code. A total of 708 and 713 microwave transitions (6⩽ J ⩽40, ⩽23) belonging to the ground torsional state νt =0 and 1 have been fitted with root-mean-square (rms) deviations of 37.4kHz and 32.3kHz respectively, and 3170 pure rotational transitions in the far-infrared range (12⩽ Jmax ⩽65, 0⩽ ⩽48) belonging to νt =0 and 1 have been fitted with a rms deviation of 0.00017cm−1, using 35 parameters. Since in the far-infrared spectral range, the A–E internal rotor splittings have not been observed for the transitions belonging to the torsional ground νt =0 state of the cis-methyl nitrite species, another fit was performed on those lines, using a Watson type Hamiltonian for comparison. [Copyright &y& Elsevier]

The fundamental S–S stretching mode ν 3 of disulfur monoxide, S 2 O, located at 679 cm −1 , has been investigated using Fourier-transform far-infrared spectroscopy at the SOLEIL synchrotron facility. A spectroscopic analysis has been performed using an Automated Spectral Assignment Procedure (ASAP) which permits accurate determination of more than 2000 energy levels from ν 3 . In addition, the ν 3 + ν 2 − ν 2 hot band was observed for the first time and some 500 corresponding energy levels were assigned. The high-resolution synchrotron study was complemented with pure rotational spectra of S 2 O in the ( v 1 , v 2 , v 3 ) = (0, 0, 1) vibrational state observed in the frequency range from 250 to 280 GHz using a long-path absorption cell. From these combined measurements, extensive molecular parameter sets have been determined and precise band centers have been derived for both vibrational bands. [ABSTRACT FROM AUTHOR]

• Far IR high resolution O 2 spectrum is recorded by FTS at SOLEIL synchrotron. • 26 weak pure rotational magnetic dipole transitions are measured. • 45 years-old previous line intensities measurements are validated. • Significant reduction of HITRAN intensity uncertainty is suggested. The oxygen absorption spectrum in the 50–170 cm-1 spectral range is studied at the AILES beam line of the SOLEIL synchrotron with a Fourier transform spectrometer equipped with a 151-m multipass gas cell. The spectrum recorded at room temperature (23.15°C) with a pressure of 19.76 Torr is formed by weak pure rotational magnetic dipole transitions. Line parameters of 26 lines are derived and compared to literature values. In particular, measured line intensities confirm the 45 years-old previous values reported by Boreiko et al. (J. Quant. Spectrosc. Radiat. Transfer 32 (1984)109–117). The agreement with HITRAN intensities (within 1% level for the strongest lines) indicates that the 20% HITRAN error estimate was overly cautious: we show that the error is more likely within 2%. Image, graphical abstract [ABSTRACT FROM AUTHOR]