Soutenance de thèse - Divita Gupta

Rate Coefficients and Branching Ratio Measurements for Reactions of Astrochemical Relevance Involving CN Radicals

Low-temperature laboratory studies to explore CN radical reactions relevant to interstellar environments were performed using the CRESU technique coupled with pulsed laser photolysis– laser induced fluorescence and chirped–pulse Fourier transform microwave spectroscopy.

Rate coefficients for the reaction of CN radical with methanol, benzene, and toluene were measured from 296 K down to 16 K using the pulsed–laser photolysis–laser induced fluorescence technique by monitoring the CN radical concentration over time. A negative temperature dependence was observed for the reaction of methanol with the CN radical typical of what has been seen previously for other radical–neutral reactions that do not possess potential energy barriers. The measurements significantly deviate from the values currently in the Kinetics Database for Astrochemistry (KIDA) that are used in various astrochemical models and recommendations for updated values are provided. I will cover the kinetics measurements for the reaction of two aromatic molecules, benzene and toluene, with CN radical which shows that these reactions remain fast down to 16 K. The potential interstellar implications of these measurements in the light of the recent detection of cyano–substituted benzene in the interstellar medium are discussed.

The second part of my work was focused on investigating the product channel–specific branching ratios for the reaction of CN radical with propene at 35 K. These experiments were performed using the recently developed E–band chirped pulse FT-microwave spectrometer integrated with the CRESU technique allowing detection of one product channel, which is the first measurement of its kind for this reaction below room temperature. The results for this reaction will be presented along with the future direction for this study.