FORMATION OF RADICAL CATIONS OF POLYIODOMETHANES - A PULSE-RADIOLYSIS STUDY

The transient optical absorption band (Xmax = 380 nm, t 1/223 μs and e = 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+ (Xmax = 380 and 570 nm, t1/2 = 3 μs and ε570 = 2150 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 CH2I 2+ have been determined to be 2.1 × 109 and 6.0 × 109 dm3 mol-1 s-1 respectively. Cl2- has been found to oxidize CH 2l2 to CH2l2+ with a bimolecular rate constant of 1.7 × 108 dm3 mol -1 s-1. CH2l2+ is a good oxidant and oxidizes l-, 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 1/2 G(-CH2I2). The transient optical absorption bands observed on pulse radiolysis of CH2I2 and CHI3 in 1,2-dichloroethane have been assigned to CH2l2+ (γmax = 380 and 590 nm) and CHI3+ (γmax = 400 and 610 nm).