Laser-Initiated Chemical Chain Reactions: Termination Kinetics of the Cl2/HBr/NO Chain System

Article abstract of DOI:10.1021/j100127a013

The termination steps of the laser-initiated Cl2/HBr chemical chain reaction have been studied via time-resolved infrared chemiluminescence (IRCL) from the vibrationally excited HCl(υ) product molecules.Laser photolysis/IRCL experiments were conducted at 298 +/- 3 K in slowly flowing gas mixtures of Cl2, HBr, and NO diluted in Ar.The termolecular association of Br^. with NO (M = Ar) competed with the second propagation step for the Br^. chain carrier, thereby terminating the chain.The resulting pseudo-firdt-order decayy rates of the steady-state IRCL signal were obtained with 6-60 Torr of argon as the third-body collision partner.T he low-pressure rate coefficient for Br^. + NO + Ar -> BrNO + Ar was determined to be k₃ = 8⁺³_-4 * 10^-32 cm⁶ molecule^-2 s^-1 at 298 K.The present work demonstrates the utility of the laser-initiation/IRCL method in kinetic measurements of chain termination rates.This technique may be applicable as a competitive method for measuring rate coefficients for other radicals that can be incorporated into a chain reaction via H atom abstraction.