Kinetic Studies of Halogen Containing Radicals in the Aqueous Phase

Halogen Radical Oxidants in Natural and Engineered Aquatic Systems

“…Once generated, halogen radicals react via an array of propagation and termination reactions. Halogen radicals react with halides to interconvert between monatomic (X • ) and diatomic (X 2 •– , XY •– ) radical species (eq , , ) ,,− or with H 2 O/OH – to form • OH (eq –). ,,, In most halide-containing environmental waters, X 2 •– / XY •– dominate relative to X • , and Br-containing radicals are present in higher abundance relative than Cl-only radicals when [Br – ]/[Cl – ] > 5 × 10 –5 . As indicated by eq –, halogen radicals are present at higher concentrations relative to • OH in more acidic solutions (SI Figure S1).…”

“…In addition, the generation of halogen radicals due to halide oxidation by 3 SENS* has also been explored, primarily by monitoring the loss of 3 SENS*. , Because the loss of 3 SENS* includes both quenching to ground-state as well as free radical generation, 3 SENS* loss provides an upper limit on halogen radical generation by this pathway. Time-resolved techniques are also used to quantify rate constants for halogen radical interconversion reactions, ,,,,, reactions with the carbonate system (i.e., to yield CO 3 •– ), and radical termination reactions. ,,, While these reactions have been predominantly studied in single-halogen systems, a few studies have investigated reactions in mixed-halogen systems. ,, …”

“…20,30,33,50 While these reactions have been predominantly studied in single-halogen systems, a few studies have investigated reactions in mixed-halogen systems. 39,47,48 Time-resolved techniques are also employed to determine bimolecular rate constants for the reaction of halogen radicals with different substrates. The most straightforward approach is to monitor the decay of the halogen radical (e.g., X 2…”