Measurements of formation rates of newly-detected carbon-rich molecules in star-forming regions

The universe is chemically complex. Around 330 molecules have been observed in space with 45 new molecules detected in just the past three years, many of which are exotic and contain a variety of functional groups, some akin to those appearing in living systems. The observations are made by modern telescopes, using a single dish or array of dishes on the ground, or by space-borne telescopes. These molecules are synthesised from smaller building blocks, either on the surface of grains or in the gas-phase. In this project we will focus on carbon rich molecules which have been discovered by these telescopes in the last 5 years, with the overall aim of understanding how they are formed under the extreme conditions encountered in space. Currently these molecules have no known/studied formation rates and are thus not present in current astrochemical networks which attempt to explain their chemistry.
In this project we will investigate the gas-phase chemistry of these newly detected carbon-rich species by determining the rates of nine key reactions that have been proposed for their formation, using a combination of laboratory measurements and calculations using quantum theory. The new data set of kinetic parameters for these reactions will be exploited using a state-of-the-art astrochemical model employing the most recent release of the UMIST Database for Astrochemistry.
It is crucial to determine the kinetic data, which consist of rate coefficients which are an inherent measure of how quickly a reaction proceeds, under relevant conditions found in interstellar and circumstellar environments, which can reach as low as 10 degrees above absolute zero (10 K). In the laboratory we will use an established apparatus, consisting of a Laval nozzle which is able to generate a uniform flow of gas at temperatures as low as 24 K, and which has a proven track record of determining the kinetics of many reactions of molecules observed in space under relevant conditions. Reactive species (small carbon-based species such as carbon atoms) will be generated by pulsed lasers in the uniform flow, and monitored in real time using laser-spectroscopic methods as they react with larger, more stable carbon-rich molecules added to the flow, and which are proposed to increase the length of the carbon chain. We will experimentally determine the kinetics over a range of temperatures, and will also quantify the formation of hydrogen atoms, again using lasers, that are expected to form from these reactions.
To interpret the kinetic data, and to predict behaviour at temperatures outside the range achievable in the laboratory, we will perform complementary theoretical calculations using quantum mechanics to determine kinetic parameters, including the identity and yield of all of the products which may form. The new laboratory and theoretical kinetic data will then be used within a detailed gas-grain astrochemical model which has been established at Leeds, to provide predictions of the abundance of carbon rich molecules for comparison with telescope observations. In this way we can quantify the impact of the newly studied reactions on these molecules.
Although it is challenging to study kinetics at very low temperatures, we have chosen reactions to study which should be fast at the very low temperatures found in space, either by analogy with reactions of other carbon-based species or via theoretical estimates which suggest a barrierless process. Hence we are confident it will succeed.