Knowledge Bank

CH$2$I$2$ plays an important role in atmospheric chemistry as a significant natural source of organohalide compounds. The photodissociation dynamics of CH$2$I$2$ in the ultraviolet range of 277-305 nm via the two lowest B$1$ excited states has been well studied using one-color velocity map ion imaging (VMI) and photofragment translational spectroscopy. In this two-color experimental study, CH$2$I$2$ is photodissociated by 248 nm via the B$2$ or A$1$ excited states to give rise to CH$2$I and I ($2$P$3$$\mathrm{<mrow\; data-mjx-texclass="ORD">/</mrow>}$$2$) or I$\ast$ ($2$P$1$$\mathrm{<mrow\; data-mjx-texclass="ORD">/</mrow>}$$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 CH$2$I fragment, consistent with prior infrared emission results of Baughcum and Leone. \textbf{72}, 6531 (1980).} 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 CH$2$I fragment is of particular interest because of its subsequent reaction with O$2$ in a near thermo-neutral reaction to produce the smallest Criegee intermediate, CH$2$OO. We anticipate that the internal energy contained in CH$2$I will likely be carried into CH$2$OO.