Kinetics of Formation of Chloride Ions in Atmospheric Pressure Flames by Way of HCl+e−⇆+Cl−

Abstract

Gas phase negative ions are of great importance in discharges1 and the upper atmosphere2. They may also be produced in combustion systems in amounts greater than those for thermodynamic equilibrium, with the underlying chemi-ionization effect3 being of possible use in the large scale generation of electric power by magnetohydrodynamics (MHD)4. Chloride ions also can play a role in the exhaust plume of a rocket during the undesirable modulation and attenuation of radio signals by the free electrons present. The importance of Cl− in this situation is, however, quite unclear5 because of the great uncertainty in the kinetics of its formation. It now seems certain3,6 that chloride ions in combustion systems are usually produced from HCl (the dominant chlorine-containing species in fuel-rich flames) by a dissociative attachment mechanism (1), rather than the slower three-body scheme (2), which involves any molecule M as a chaperon illustration The available experimental evidence on k1 the rate constant of reaction (1), is conflicting. Buchel'nikova's work7 suggests that k=10−10 exp(−104/T)ml per molecule s−1, whereas that of Fehsenfeld et al.8 on the reverse of reaction (1) indicates k1=2×10−7 exp(−104/T) in identical units. Also an estimate of at least 10−8 ml per molecule s−1 has been made6 for the pre-exponential factor. This study is addressed to resolving these discrepancies. Open image in new window