Cyanopolyynes are a series of CN-terminated linear acetylenic carbon chains of generic formula H(C≡C)nC≡N. They are widely observed along with related polyyne chains in space environments including cold molecular clouds, star-forming regions, photon-dominated regions, and the ejecta of evolved stars. We have studied possible formation routes of a prototypical member of this series, HC5N, using a combination of established and innovative spectroscopic-kinetic tools, along with new theoretical calculations. Three reactions leading to HC5N have been identified and studied: C2H + HC3N → HC5N + H CN + HC4H → HC5N + H C3N + HC2H → HC5N + H Three different laser photochemical and spectroscopic schemes have been employed to study the kinetics of these three reactions over the 25—293 K temperature range within the extremely cold gas-phase environment provided by the CRESU (Reaction Kinetics in Uniform Supersonic Flow) technique. In particular, the reaction kinetics of the C3N radical has been studied for the first time at any temperature using BrC3N as a photolytic precursor. High accuracy ab initio quantum chemical calculations coupled with variational (two-)transition state theory calculations were also performed for each reaction. We will discuss these experimental and theoretical results and also present the CRESUCHIRP project, which aims to apply the new CPUF (Chirped Pulse in Uniform supersonic Flow) kinetic-spectroscopic technique to the direct detection of low temperature reaction products such as HC5N.

Formation of HC5N in space environments

256th National Meeting (2018)

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