VUV Photofragmentation of CH2I2: The [CH2I-I]o+ Iso-diiodomethane Intermediate in the I-Loss Channel from [CH2I2]o+

Diiodomethane is an important halocarbon responsible for several atmospheric processes like ozone depletion and aerosol particle formation. Despite this, the thermochemical data and a detailed analysis of the pathways for the decomposition of this halomethane and its molecular ion [CH2I2]o+ are scarce. In this paper an investigation of the photodissociation dynamics of the CH2I2 molecule focused on the I-loss channel by the photoelectron-photoion coincidence (PEPICO) technique and computational methods is reported. The experimental results show that upon VUV irradiation the dissociation of the lower electronic ionic states of diiodomethane leads only to the CH2I+ ion and the I atom. The theoretical calculations point out that isomerization of [CH2I2]o+ into iso-diiodomethane [CH2I-I]o+ may play an important role in the emission of iodine atom as compared to direct C-I bond breaking.