High temperature reaction kinetics of CN(v = 0) with C2H4 and C2H6 and vibrational relaxation of CN(v = 1) with Ar and He.

The investigation of the chemical complexity of hot environments, ranging from combustion flames to circumstellar envelopes of evolved stars, relies on the determination of the reaction kinetics and product branching ratio. We have designed a chemical reactor for the exploration of high temperature chemistry. This apparatus is employed in the present study to measure the reaction kinetics of the CN radical with C2H4 and C2H6 over the 300-1200 K temperature range. In our setup and in some environments, the CN radical is partially produced in a vibrationally excited state, before relaxing by collision with the surrounding gas. We complement the experimental kinetic studies of hydrocarbons reactions with CN(v = 0) with a theoretical study of vibrational relaxation of CN(v = 1) by He and Ar atoms, the main collisional partners in our apparatus. Calculations are carried out to determine the collisional elastic and inelastic cross sections versus the kinetic energy as well as the corresponding vibrationally elastic and inelastic rate coefficients. The results are compared with empirical calculations and with a few experimental observations. The range of validity of the empirical model is discussed and potential applications sketched.