A Reinvestigation of the Laser-Initiated Cl2/HBr Chain Reaction: Absolute Rate Constants and the ν = 2/ν = 1 Ratio from Cl+HBrHCl(ν)+Br

Article abstract of DOI:10.1021/j100297a016

The Cl2/HBr chain reaction is reinvestigated by using real time state-selected observations of Δν = -1 chemiluminescence from the HCl(ν) products following pulsed laser photolysis of Cl2.These state-selected observation are analyzed with a more complete kinetic treatment to obtain room temperature rate constats for the chain propagation steps and the vibrational deactivation of HCl(ν=1,2) by HBr.The chain propagation rate constants are k_R1=(1.02+/-0.15)E-11 and k_R2=(1.1+/-0.4)E-15 cm³ molecule^-1s^-1, respectively , for Cl+HBr<*>HCl(ν)+Br and Br+Cl2<*>BrCl+Cl.Rate constants for vibrational deactivation of HCl(ν=1) and HCl(ν=2) by HBr are k_V1=(1.06+/-0.16)E-12 and k_V2=(2.09+/-0.50)E-12 cm³ molecule^-1 s^-1.Relative intensity measurements of the HCl ν=2<*>1 and 1<*>0 vibrational fluorescence are used to obtain an HCl(ν) product branching ratio, N_ν=2/N_ν=1=0.40+/-0.06.The kinetic analysis indicates that broad-band observations of infrared chemiluminescence may lead to erroneous rate constant determinations because of vibrational cascade, whereas the detection of the individual vibrational states leads to correct results.