JULIA H. LEHMAN, HONGWEI LI AND MARSHA I. LESTER, Department of Chemsitry, University of Pennsylvania, Philadelphia, PA 19104-6323.
CH2I2 plays an important role in atmospheric chemistry as a significant natural source of organohalide compounds. The photodissociation dynamics of CH2I2 in the ultraviolet range of 277-305 nm via the two lowest B1 excited states has been well studied using one-color velocity map ion imaging (VMI) and photofragment translational spectroscopy. In this two-color experimental study, CH2I2 is photodissociated by 248 nm via the B2 or A1 excited states to give rise to CH2I and I (2P3/2) or I* (2P1/2). The iodine atoms are then state selectively ionized using a (2+1) resonance-enhanced multiphoton ionization process near 310 nm and detected by VMI. Preliminary results show about 85% of the available energy is being funneled into the internal energy of the CH2I fragment, consistent with prior infrared emission results of Baughcum and Leone. The anisotropy parameter derived from the image indicates this is a fast dissociation process and reflects the character of the electronic transition. The internal energy distribution of the CH2I fragment is of particular interest because of its subsequent reaction with O2 in a near thermo-neutral reaction to produce the smallest Criegee intermediate, CH2OO. We anticipate that the internal energy contained in CH2I will likely be carried into CH2OO.