15min:

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 (²P_3/2) or I^* (²P_1/2). 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.