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

Abstract

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.

Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

“…97 In the astrochemical context, the production of CN radical is generally attributed to the photolysis of HCN. 98 For higher temperatures, experimental techniques have measured kinetics of CN reactions with small linear hydrocarbons up 1200 K. 17,18 In combustion chemistry, the CN radical is a key species in the incorporation of nitrogen into large carbon structures and is also implicated in the fate of NO and many other reactions. 64 Nitrile species are also important in the combustion of biofuels.…”

“…The CN + C 2 H 4 rate coefficients have been reported for a large range of temperatures including down to 25 K 96,100 and up to ~1200 K. 18 The 298 K rate coefficient is reported to be 2. molecule -1 s -1 . This study also includes a computational RRKM analysis to predict the products and rationalize the experimental measurements.…”

A combined crossed molecular beams and theoretical study of the reaction CN+C2H4

“…For all these reasons, CN reactions with small unsaturated hydrocarbons have been widely investigated in kinetics [1,[16][17][18][19][20][21][22][23] and reaction dynamics [24][25][26][27][28][29][30][31][32] experiments. More specifically, the reaction CN + C 2 H 4 was found to be very fast, approaching the gas kinetics limit, at very low and high temperatures [16,23], confirming its role in cold and hot environments. Nevertheless, some uncertainties in http://dx.doi.org/10.1016/j.chemphys.2014.12.014 0301-0104/Ó 2015 Elsevier B.V. All rights reserved.…”

High‐temperature kinetics of the reaction between CN and hydrocarbons using a novel high‐enthalpy flow tube

“…According to the Schwartz–Slawsky–Hersfeld (SSH) model (see, e.g., Ref. 32), which aims at evaluating the rate constants for the vibrational–translational energy exchange, the relaxation becomes even much slower in Ar 33. We can safely assume that in our experiment the CN ( v = 1) population will not relax within the probing short timescale (∼100 μs) and will then not perturb the measurement of the time evolution of the CN ( v = 0) population.…”