Structural determination of a transient isomer of CH2I2 by picosecond X-ray diffraction

Ultrafast time-resolved spectroscopic studies of complex chemical reactions in solution are frequently hindered by difficulties in recovering accurate structural models for transient photochemical species. Time-resolved x-ray and electron diffraction have recently emerged as techniques for probing the structural dynamics of short lived photointermediates. Here we determine the structure of a transient isomer of photoexcited CH2I2 in solution and observe the downstream reactions of the initial photoproducts. Our results illustrate how geminate recombination proceeds via the formation of a transient covalent bond onto the iodine atom remaining with the parent molecule. Further intramolecular rearrangements are thus required for the CH2I-I isomer to return to CH2I2. The generation of I-3(-) from those iodine radicals escaping the solvent cage is also followed with time.