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We present the first rotationally resolved spectra of adamantane (C10H16) applying gas-phase Fourier transform infrared (IR) absorption spectroscopy. High-resolution IR spectra are recorded in the 33-4500 cm-1range using as source of IR radiation both synchrotron radiation (at the AILES beamline of the SOLEIL synchrotron) as well as a classical globar. Adamantane is a spherical top molecule with tetrahedral symmetry (Td point group) and has no permanent dipole moment in its vibronic ground state. Of the 72 fundamental vibrational modes in adamantane, only 11 are IR active. Here we present rotationally resolved spectra for seven of them: ν30, ν28, ν27, ν26, ν25, ν24, and ν23. The typical rotational structure of spherical tops is observed and analyzed using the STDS software developed in the Dijon group, which provides the first accurate energy levels and rotational constants for seven fundamental modes. Rotational levels with quantum numbers as high as J = 107 have been identified and included in the fit leading to a typical standard deviation of about 10-3 cm-1. [ABSTRACT FROM AUTHOR]

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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: As a tetrahedral molecule, methane has no permanent dipole moment. Its spectrum, however, displays faint absorption lines in the THz region, due to centrifugal distorsion effects. This is important for planetary applications since this region is used to measure methane concentration in some planetary atmospheres, in particular on Titan. Up to now, all measurements relied either on some old low resolution infrared absorption spectra, or on high resolution Stark measurements for low J values only. Even if these results have been reexamined recently [Wishnow EH, Orton GS, Ozier I, Gush HP. The distorsion dipole rotational spectrum of CH4: a low temperature far-infrared study. J Quant Spectrosc Radiat Transfer 2007;103:102–17], it seemed highly desirable to obtain much more precise laboratory data. The high-intensity synchrotron radiation, combined with a 151.75±0.1m optical path in a White cell and a Bruker IFS 125 HR FTIR spectrometer at the AILES beamline of SOLEIL, enabled us to record this very weak spectrum at high resolution for the first time. Spectra were obtained in the 50–500cm−1 wavenumber range at 296K and 9.91, 20, 50 and 100mbar with a resolution of 0.00074, 0.00134, 0.0034 and 0.0067cm−1 (FWHM of the sinc function), respectively. The rotational clusters are fully resolved and the good signal-to-noise ratio has enabled precise measurements of transition intensities (92 cold band lines and 96 Dyad–Dyad hot band lines, with normal abundance intensities in the range 2×10−26–1×10−24 cm−1/(molcm−2)), yielding an accurate determination of the dipole moment derivatives. Such results should allow a better determination of CH4 concentration in planetary objects. [Copyright &y& Elsevier]

We present laboratory measurements of the water vapor continuum absorption in the far-IR region from 14 to 200 cm −1 . These data were obtained using a Fourier Transform spectrometer IFS125 HR associated with a multipass absorption cell and with the synchrotron far-IR broadband radiation extracted by the AILES beamline of SOLEIL facility. The spectra were recorded at room temperature (296 K) and pressures ranging from 2.73 to 15.1 mbar. A comparison with presently available experimental data is presented and the nature of the possible contributors to the continuum is discussed. The new data considerably extend and unify diverging results of previous measurements of the continuum performed in several spots within the range from about 3 cm −1 up to 84 cm −1 . The new evidence of significant contribution of the water dimer to the continuum formation is revealed in the range of 14–35 cm −1 . Analysis of the possible cause of the observed continuum indicates that its significant part in the range of the maximum intensity of water monomer rotational spectrum cannot be explained within the current understanding of the continuum origin. [ABSTRACT FROM AUTHOR]

We report the pure rotation spectrum of HN2+ as measured by Fourier transform (FT) absorption spectroscopy in the 20-40 cm−1 spectral range. The cations are produced in a liquid nitrogen cooled hollow cathode discharge cell developed on the AILES beamline of synchrotron SOLEIL. The setup was optimized by recording rotation-vibration spectra of H3+ (with the ν2 band centered at about 2521 cm−1), HN2+ (with the ν1 band centered at about 3234 cm−1), and HCO+ (with the ν1 band centered at about 3089 cm−1). Many rotation-vibration lines have been assigned for each ion and five pure rotational transitions have been detected for HN2+. These results demonstrate the feasibility of recording far-infrared spectra of cationic species using FT broad band spectroscopy associated with the bright synchrotron radiation continuum as an alternative to laser-based frequency tunable techniques. [ABSTRACT FROM AUTHOR]

Abstract: Pure rotational transitions of OH and SH radicals have been recorded in the THz spectral range using cw-THz and synchrotron-based FT-FIR techniques. Line lists on these radicals have been completed in the three and two lowest vibrational states for OH and SH, respectively. Furthermore, the hyperfine structure of OH and SH has been observed for the first time using infrared IR FT-spectroscopy, and at frequencies higher than 1THz, respectively. A combined fit has been made for each of these radicals including v =0, 1 and 2 for OH and v =0 and 1 for SH. [Copyright &y& Elsevier]

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]

Spherical-top tetrahedral species like CH 4 , SiH 4 , CF 4 , …possess no permanent dipole moment. Therefore, probing their pure rotation spectrum is very challenging since only a very weak dipole moment can be induced by centrifugal distortion and/or rovibrational interaction. If some Q branch lines have been recorded thanks to microwave techniques, R branch lines in the THz region have been poorly explored until recently. In previous studies, we have reported the pure rotation THz spectrum of cold and hot band lines of methane recorded at the SOLEIL Synchrotron facility. Here, we present the first recorded THz spectrum of the R branch of CF 4 , a powerful greenhouse gas, in its v 3 = 1 state. This Fourier transform spectrum covers the R ( 20 ) to R ( 37 ) line clusters, in the 20–37 cm −1 spectral range. It was recorded thanks to a 150 m multiple path cell at room temperature. We could estimate the vibration-induced dipole moment value and also include the recorded line positions in a global fit of many CF 4 transitions. [ABSTRACT FROM AUTHOR]

Methoxyphenols are emitted in the atmosphere from biomass burning and recent works have shown the potential role of these oxygenated aromatic species in the formation of secondary organic aerosols. IR spectroscopic data that would enable their remote measurement in the atmosphere remain scarce in the literature. Room temperature Far-IR cross-sections of 4 methoxyphenols (2-methoxyphenol or guaiacol, 3-methoxyphenol, 4-methoxyphenol and 2,6-dimethoxyphenol or syringol) have been determined using the THz synchrotron radiation available at SOLEIL. Mid- and near-IR regions have also been investigated with a conventional Fourier transform IR setup and allowed to provide a set of vibrational cross-sections of the studied methoxyphenols. Finally, gas-phase cross sections of two nitroguaiacol isomers (4-nitroguaiacol and 5-nitroguaiacol), two intermediate products involved in the formation of secondary organic aerosols have been measured in the mid- and near-IR with a heated multi-pass cell. Harmonic and anharmonic density functional theory calculations were carried out for all the studied compounds and allowed a full assignment of the recorded rovibrational bands. [ABSTRACT FROM AUTHOR]

The fundamental vibrational bending mode ν 2 of disulfur monoxide, S 2 O, and the associated hot band 2 ν 2 - ν 2 have been observed at high spectral resolution for the first time at the SOLEIL synchrotron facility using Fourier-transform far-infrared spectroscopy. This transient species has been produced in a radio-frequency discharge by flowing SO 2 over elemental sulfur. The spectroscopic analysis has been performed using the newly developed Automated Spectral Assignment Procedure (ASAP) which has enabled the accurate determination of more than 3500 energy levels of the v 2 = 1 and 2 vibrational states. The procedure provides a fast and convenient way to analyze large data sets in a straightforward manner, if one of the two vibrational states involved in the transition is accurately known from prior work. In addition to the high-resolution synchrotron study, pure rotational spectra of S 2 O in the v 2 = 1 and 2 vibrational states were observed in the frequency range 250–500 GHz by absorption spectroscopy in a long-path absorption cell. From these combined measurements, extensive molecular parameter sets have been determined, including full sets of sextic and two octic centrifugal distortion terms. Highly accurate band centers (to better than 10 - 5 cm −1 ) have been derived for both vibrational bands. [ABSTRACT FROM AUTHOR]

Abstract: Absolute intensities of about 120 lines of the 12C2H2 molecule are reported for the ν 4–ν 5 band between 65 and 192cm–1, with an average accuracy of 5%. Vibrational transition dipole moment squared values and empirical Herman–Wallis coefficients are obtained allowing modelling the rotational dependence of the transition dipole moment squared. Special care is taken to accurately determine an apparatus function for the Bruker IFS 125-HR coupled to the synchrotron SOLEIL far infrared AILES beamline in order to minimize its effects on the line parameter retrieval. [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]