The first year of the project (2016-17) was dedicated to building a new laboratory in Rennes, recruiting staff, and designing the chirped pulse microwave spectrometers. Following on from this during 2018-19, construction of the new instruments was commenced. LIF experiments were performed on reactions of astrochemical interest resulting in two publications. During 2019-20, the first chirped pulse microwave spectrometer (operating in the so-called E-band, covering frequencies from 60 to 90 GHz) was assembled and tested resulting in a publication. These tests revealed a need to operate at lower pressures (see Figure on the effect of pressure on OCS Free Induction Decays or FIDs), and significant modifications were proposed to the original project to mitigate this effect. These included skimmed molecular beam sampling of the reaction products, as well as a more long-term project for a high repetition rate pulsed CRESU. In addition, a dedicated CRESU chamber was designed and built. During 2020-2021, the second spectrometer (operating in the Ka band) was constructed and tested resulting in a publication. The first reaction products from the CN + C2H6 and CN + C2H2 reactions were observed directly in cold He and Ar flows (at 10 K and 30 K), and the resulting article is nearing submission at the time of writing. The observation of HCN (see Figure for preliminary results) and its unstable isomer HNC from laser photolysis of acrylonitrile in cold (10-70 K) He flows enabled measurement of He pressure broadening cross sections in situ by CPFTMW time-resolved spectroscopy, providing vital benchmarking of theoretical calculations essential to the interpretation of astronomical observations. The COVID-19 pandemic resulted in significant delays, but we were able to implement the skimmed molecular beam sampling chamber and fully characterise it by detection of acrylonitrile product from the CN + C2H4 reaction, and another article describing this work is in preparation. During the last year of the project (2021-22) reaction products from the CN + C3H6 reaction were detected and quantified at two different temperatures (35 K and 50 K), and experiments to investigate pressure dependence are currently underway. This reaction is of significant astrochemical interest and is thought to be occurring in cold molecular clouds. The HNC/HCN pressure broadening results along with theoretical calculations by colleagues here in Rennes were published in Nature Chemistry. Finally, we completed construction of a prototype pulsed CRESU with a hydraulically actuated spinning disk valve (see photo), and obtained preliminary results yielding a 5 K He flow at much lower pressure than before (see Figure). This will provide the basis for further projects.
The results of this project have been disseminated by team members in a large number (in excess of 50) of contributed and invited oral presentations, and poster presentations as well as by peer-reviewed scientific publications, both already appeared (7) and in preparation (3-5), as well as via the project website.
