The microwave spectrum of 2,5-dimethylfuran was recorded using two pulsed molecular jet Fourier transform microwave spectrometers which cover the frequency range from 2 -40 GHz. The internal rotations of two equivalent methyl tops with a barrier height of approximately 439.15 cm −1 introduce torsional splittings of all rotational transitions in the spectrum. For the spectral analysis, two different computer programs were applied and compared, the PAM-C2v-2tops code based on the principal axis method which treats several torsional states simultaneously, and the XIAM code based on the combined axis method, yielding accurate rotational and centrifugal distortion constants. The experimental work was supplemented by quantum chemical calculations. Two-dimensional potential energy surfaces depending on the torsional angles of both methyl groups were calculated and parametrized.

Catechol is an oxygenated aromatic volatile organic compound and a biogenic precursor of secondary organic aerosols. Monitoring this compound in the gas phase is desirable due to its appreciable reactivity with tropospheric ozone. From a molecular point of view, this molecule is attractive since the two adjacent hydroxy groups can interchangeably act as donor and acceptor in an intramolecular hydrogen bonding due to the tunnelling between two symmetrically equivalent structures. Using synchrotron radiation, we recorded a rotationally-resolved Fourier Transform far-infrared (IR) spectrum of the torsional modes of the free and bonded −OH groups forming the intramolecular hydrogen bond. Additionally, the room temperature, pure rotational spectrum was measured in the 70–220 GHz frequency range using a millimeter-wave spectrometer. The assignment of these molecular transitions was assisted by anharmonic high-level quantum-chemical calculations. In particular, pure rotational lines belonging to the ground and the four lowest energy, vibrationally excited states were assigned. Splitting due to the tunnelling was resolved for the free −OH torsional state. A global fit combining the far-IR and millimeter-wave data provided the spectroscopic parameters of the low-energy far-IR modes, in particular those characterizing the intramolecular hydrogen bond dynamics.

Even if on-board mm-wave/THz heterodyne receivers have been developed to measure greenhouse gases (GHGs) atmospheric profiles, rotational spectroscopy rests under-exploited for their monitoring unlike IR rovibrational spectroscopy. The present study deals with the ability of THz spectroscopy using long interaction path-lengths for GHG laboratory investigations. High-resolution THz signatures of non-polar greenhouse molecules may be observed by probing very weak centrifugal distortion induced rotational transitions. To illustrate, new measurements on CH4 and CF4 have been carried out. For CH4, pure rotational transitions, recorded by cw-THz photomixing up to 2.6 THz in a White type cell adjusted to 20 m, have allowed to update the methane line list of atmospheric databases. Concerning CF4, Fabry-Perot THz absorption spectroscopy with a km effective pathlength was required to detect line intensities lower than 10−27 cm−1/(moleccm−2). Contrary to previous synchrotron-based FT-FIR measurements, the tetrahedral splitting of CF4 THz lines is fully resolved. Finally, quantitative measurements of N2O and O3 gas traces have been performed in an atmospheric simulation chamber using a submm-wave amplified multiplier chain coupled to a Chernin type multi-pass cell on a 200 m path-length. The THz monitoring of these two polar GHGs at tropospheric and stratospheric concentrations may be now considered.

Methoxyphenols (MP) are a significant component of biomass burning emissions which mainly exists in our atmosphere in the gas phase where they contribute to the formation of secondary organic aerosols (SOA). Rovibrational spectroscopy is a promising tool to monitor atmospheric MPs and infer their role in SOAs formation. In this study, we bring a new perspective on the rovibrational analysis of MP isomers by taking advantage of two complementary devices combining jet-cooled environments and absorption spectroscopy: the Jet-AILES and the SPIRALES setups. Based on Q-branches frequency positions measured in the Jet-AILES FTIR spectra and guided by quantum chemistry calculations, we propose an extended vibrational and conformational analysis of the different MP isomers in their fingerprint region. Some modes such as far-IR out-of-plane-OH bending or mid-IR in-plane-CH bending allow to assign individually all the stable conformers. Finally, using the SPIRALES setup with three different EC-QCL sources centered on the 930-990 cm −1 and the 1580-1690 cm −1 ranges, it was possible to proceed to the rovibrational analysis of the ν 18 ring in-plane bending mode of the MP meta isomer providing a set of reliable excited state parameters which confirms the correct assignment of two conformers. Interestingly, the observation of broad Q-branches without visible P-and R-branches in the region of the CC ring stretching bands was interpreted as being probably due to a vibrational perturbation. These results highlight the complementarity of broadband FTIR and narrowband laser spectroscopic techniques to reveal the vibrational conformational signatures of atmospheric compounds over a large infrared spectral range.