Gas phase chemical kinetics at high temperature of carbonaceous molecules: application to circumstellar envelopes

Details Gas phase chemical kinetics at high temperature of carbonaceous molecules: application to circumstellar envelopes Gas phase chemical kinetics at high temperature of carbonaceous molecules: application to circumstellar envelopes

May 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p..97b&link_type=abstract

The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole

Astronomy and Astrophysics

Astronomy

Scientific paper

Circumstellar shells of evolved stars are a theater of extremely rich physical and chemical processes. More than seventy molecules of varied nature have been identified in the envelopes through their spectral fingerprints in the microwave or far infrared regions. Many of them are carbon chain molecules and radicals and a significant number are unique to the circumstellar medium. However, observational data remain scarce and more than half of the detected species have been observed in only one object, the nearby carbon star IRC + 10216. Chemical kinetic models are needed to describe the formation of molecules in evolved circumstellar outflows. Upcoming terrestrial telescopes such as ALMA will increase the spatial resolution by several orders of magnitude and provide a wealth of data. The determination of relevant laboratory kinetics data is critical to keep up with the development of the observations and of the refinement of chemical models. Today, the majority of reactions studied in the laboratory are the ones involved in combustion and concerning light hydrocarbons. Our objective is to provide the scientific community with rate coefficients of reactions between abundant species in these warm environments. Cyanopolyynes from HC_2N to HC_9N have all been detected in carbon rich circumstellar envelopes in up to 10 sources for HC_3N. Neutral-neutral reactions of the CN radical with unsaturated hydrocarbons could be a dominant route in the formation of cyanopolyynes, even at low temperatures. Our approach aims to bridge the temperature gap between resistively heated flow tubes and shock tubes. The present kinetic measurements are obtained using a new reactor combining a high enthalpy source (Moudens et al. 2011) with a flow tube and a pulsed laser photolysis and laser induced fluorescence system to probe the undergoing chemical reactions. The high enthalpy flow tube has been used to measure the rate constant of the reaction of the CN radical with propane, propene, propadiene, 1,3-butadiene, and butyne over a temperature range extending from 300 to 1200 K. The majority of the reactions studied are rapid, with rate constants greater than 10-10 cm^3 molecule-1 s-1.

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