THz and submillimeter gas phase spectroscopy appears as the perfect tool for analytical chemical analysis due an exceptional degree of resolution. Despite many attractive applications such as breath analysis, environmental surveillance, food spoilage monitoring, or detection of explosive taggants, there is no commercially available versatile THz or submillimeter chemical analyzer. An important factor hindering the development of a THz chemical analyzer are the difficulties encountered to adapt ultrasensitive techniques, such as Cavity-Enhanced Techniques and Cavity Ring Down Spectroscopy to the THz and submillimeter domain. Here, we describe a low-cost high finesse THz resonator based on a low loss oversized corrugated waveguide along with high reflective photonic mirrors, and how those critical components enable a Fabry-Perot THz Absorption Spectrometer obtaining a kilometer equivalent interaction length. In addition, the intracavity optical power have allowed nonlinear interactions such as Lamb-Dip effect to be studied with a low-power emitter.
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.
Context.A recently published astronomical detection of all three doubly 13 C-substituted ethyl cyanides toward Sgr B2(N2) motivated us to investigate triple 13 C isotopic species that are expected to be also present in the ISM. Aims. We aim to present an experimental study of the rotational spectrum of triple 13 C-substituted ethyl cyanide, 13 CH 13 3 CH 13 2 CN, in the frequency range 150-990 GHz. We want to use the determined spectroscopic parameters for searching for 13 CH 13 3 CH 13 2 CN in ALMA data. The main objective of this work is to provide accurate frequency predictions to search for this molecule in the Galactic center source Sagittarius B2(N) and to facilitate its detection in space.Methods. The laboratory rotational spectrum of 13 CH 13 3 CH 13 2 CN has been recorded with the Lille's fast DDS solid-state spectrometer between 150 GHz and 990 GHz. Results. More than 4000 rotational transitions were identified in the laboratory. The quantum numbers reach J = 115 and K a = 39. Watson's Hamiltonian in the A and S reductions were used to analyze the spectra. Accurate spectroscopic parameters were determined. The rotational spectra of the 13 C containing species CH 3 CH 2 CN have been assigned, thus allowing the determination of the rotational and centrifugal distortion constants
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