The CRESU (Reaction Kinetics in Uniform Supersonic Flow) technique, combined with laser photochemical methods, has been applied with great success to gas-phase chemical kinetics at low temperatures, of particular interest for astrochemistry and cold planetary atmospheres. However, while many neutral-neutral reactions have a number of potential product channels, measurements have concentrated to date almost exclusively on the overall rate constants. There are virtually no experimental measurements of product branching ratios below 50 K, and only very limited information below room temperature.<br/>A new combination of the revolutionary chirped pulse broadband rotational spectroscopy technique, invented by Brooks Pate and co-workers, with the CRESU technique has been developed in a collaboration with the groups of Arthur Suits (U. Missouri) and Bob Field (MIT) which we have called Chirped Pulse in Uniform Flow (CPUF). Rotational cooling by frequent collisions with cold buffer gas in the CRESU flow drastically increases the sensitivity, making broadband rotational spectroscopy suitable for detecting a wide range of transient species, such as photodissociation or reaction products.<br/>In Rennes we have constructed two high-power chirped pulse spectrometers operating in the E-band (60-90 GHz) and Ka band (26.5-40 GHz) and performed experiments in continuous low temperature supersonic flows on stable molecules, photodissociation products, and the products of bimolecular reactions, including a number of CN reactions with small hydrocarbons in the range 10-30 K. I will describe this work, as well as further experimental developments to the technique to increase sensitivity by reducing the effect of pressure broadening.

Experimental determination of reaction product branching ratios at low temperatures for astrochemistry

ACS Spring Meeting 2021

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