Picosecond time-resolved resonance Raman study of CH2I-I produced after ultraviolet photolysis of CH2I2 in CH3OH, CH3CN/H2O and CH3OH/H2O solutions

Abstract

We present picosecond time-resolved resonance Raman spectroscopy experiments investigating the photo-products produced after ultraviolet photolysis of CH2I2 in CH3OH solution and in 50% CH3OH/50% H2O and 50% CH3CN/50% H2O by volume mixed solvents. We observe that isodiiodomethane (CH2I-I) is formed within several picoseconds and has a lifetime that significantly depends on the solvent system (time constant of 3.8 ns in CH3OH, 1.8 ns in 50% CH3CN/50% H2O, and 0.8 ns in 50% CH3OH/50% H2O). Our results indicate that CH2I-I can be formed via geminate recombination in aqueous environments but will have a shorter lifetime than in previous experiments done in several organic solvents. The variations in the lifetime of CH2I-I in the presence of H2O and CH3OH could be due to its chemical reaction with the O-H bond and/or possibly faster cleavage of the weak I-I bond in aqueous solutions. We briefly discuss the potential role of CH2I-I in the release of reactive halogens in aqueous environments.