Recent developments in Chirped Pulse in Uniform Flow techniques for the measurement of low temperature reaction product branching ratios

The CRESU (Reaction Kinetics in Uniform Supersonic Flow) technique has been used with great success to study the kinetics of a large number of gas-phase reactions down to very low temperatures [1]. While overall reaction rates have been measured reliably for a long time, product channel branching ratios are, for the most part, unknown at low temperatures but are needed to improve the accuracy of astrochemical models. This requires a detection technique which is sufficiently sensitive, specific and able to measure multiple species at the same time; the latter severely limiting the use of current LIF (laser-induced fluorescence) methods. A new combination of chirped-pulse spectroscopy with CRESU flows has been recently developed [2], allowing reaction products to be identified by their unique rotational spectra. In Rennes, we have constructed Ka-band and E-band spectrometers and coupled them to continuous CRESU flows, enabling measurement of cold reaction products. Recent technical advances will be presented, along with results on the detection of products from astrochemically relevant reactions of the CN radical with small hydrocarbons down to 10 K.

[1] Cooke & Sims (2019), ACS Earth and Space Chemistry, 3, 1109-1134.
[2] Abeysekera et. al. (2015), J. Phys. Chem. Lett., 6, 1599.