Terahertz Rotational Spectroscopy of Greenhouse Gases Using Long Interaction Path-Lengths

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 using long interaction path-lengths GHG laboratory investigations. High-resolution signatures non-polar molecules may be observed by probing very weak centrifugal distortion induced transitions. To illustrate, new measurements on CH4 and CF4 carried out. For CH4, pure transitions, recorded cw-THz photomixing up 2.6 in a White type cell adjusted 20 m, allowed update methane line list databases. Concerning CF4, Fabry-Perot absorption km effective pathlength was required detect intensities lower than 10−27 cm−1/(moleccm−2). Contrary previous synchrotron-based FT-FIR measurements, tetrahedral splitting lines is fully resolved. Finally, quantitative N2O O3 gas traces performed an simulation chamber submm-wave amplified multiplier chain coupled Chernin multi-pass 200 m path-length. these two polar GHGs at tropospheric stratospheric concentrations now considered.