Reactions of halogen oxides studied by flash photolysis - III. The Production and reactions of BrO and ClO radicals in the halogen-sensitized decomposition of chlorine dioxide

Abstract

The reaction between bromine atoms and chlorine dioxide, previously taken to be Br + ClO$_{2}$ $\rightarrow $ BrCl + O$_{2}$, is shown to occur by the radical mechanism Br + ClO$_{2}$ $\rightarrow $ BrO + ClO, 2BrO $\rightarrow $ Br$_{2}$ + O$_{2}$, $k_{14}$ = 1.3 $\times $ 10$^{9}$ l mol$^{-1}$ s$^{-1}$, BrO + ClO $\rightarrow $ BrCl + O$_{2}$, $k_{17}$ = 1.5 $\times $10$^{9}$ l mol$^{-1}$ s$^{-1}$. The rate constants for these reactions of BrO radicals are considerably greater than that of the bimolecular reaction of ClO radicals and the mechanisms of the reactions are discussed. The extinction coefficients for the 8, 0 and 4, 0 bands of the BrO radical at 320.8 nm and 338.3 nm are 2.32 $\times $ 10$^{3}$ and 2.83 $\times $ 10$^{3}$ l mol$^{-1}$ cm$^{-1}$ respectively. The reaction between chlorine atoms and chlorine dioxide is, likewise, almost exclusively Cl + ClO$_{2}$ $\rightarrow $ 2ClO, $k_{1}$ = 5.1 $\times 10^{9}$ l mol$^{-1}$ s$^{-1}$.