Transient isomers in the photodissociation of bromoiodomethane.

The photochemistry of halomethanes is fascinating for the complex cascade reactions toward either the parent or newly synthesized molecules. Here, we address the structural rearrangement of photodissociated CH ₂ IBr in methanol and cyclohexane, probed by time-resolved X-ray scattering in liquid solution. Upon selective laser cleavage of the C-I bond, we follow the reaction cascade of the two geminate geometrical isomers, CH ₂ I-Br and CH ₂ Br-I. Both meta-stable isomers decay on different time scales, mediated by solvent interaction, toward the original parent molecule. We observe the internal rearrangement of CH ₂ Br-I to CH ₂ I-Br in cyclohexane by extending the time window up to 3 μs. We track the photoproduct kinetics of CH ₂ Br-I in methanol solution where only one isomer is observed. The effect of the polarity of solvent on the geminate recombination pathways is discussed.