Formation of radical cations of polyiodomethanes: a pulse radiolysis study
The transient optical absorption band (λmax= 380 nm, t½= 23 µs and Îµ= 2010 dm3 mol–1 cm–1) produced on pulse radiolysis of N2O-saturated aqueous solution of CH2I2(pH 6.0) has been assigned to the OH adduct radical, CH2I2·OH. In acidic aqueous solutions, CH2I2+(λmax= 380 and 570 nm, t½= 3 µs and Îµ570= 2 150 dm3 mol–1 cm–1) has been identified as the intermediate. The rate constants for the reaction of OH radicals with CH2I2 to form CH2I2·OH and CH2I2+ have been determined to be 2.1 × 109 and 6.0 × 109 dm3 mol–1 s–1 respectively. Cl2– has been found to oxidize CH2I2 to CH2I2+ with a bimolecular rate constant of 1.7 × 108 dm3 mol–1 s–1. CH2l2+ is a good oxidant and oxidizes I–, Br–, and methyl disulphide with high rate constants close to the diffusion limit. I2 is the main stable end product formed on γ-radiolysis and its yield is equal to ½ G(-CH2I2). The transient optical absorption bands observed on pulse radiolysis of CH2I2 and CHI3 in 1,2-dichloroethane have been assigned to CH2I2+(λmax= 380 and 590 nm) and CHI3+(λmax= 400 and 610 nm).