15min:

JOSHUA P. MARTIN, JOSHUA P. DARR, W. CARL LINEBERGER, JILA and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309; ANNE B. MCCOY, Department of Chemistry, The Ohio State University, Columbus, OH 43210.

We report photofragmentation studies of mass-selected \chemICN^-(CO₂)_n (n=0-18) cluster anions following 400, 500 and 600 nm excitation. Photodissociation of \chemICN^- following excitation via a 500 nm photon results exclusively in an \chemI^- anionic photoproduct. However, excitation at either 400 nm or 600 nm results in 30% \chemCN^- and 70% \chemI^- anionic photoproducts. Complexation of \chemICN^- with two or more \chemCO₂ molecules opens a third product channel, recombination of the chromophore on the ground state, a channel that is observable at all three photon energies. The product branching ratios for photodissociation of \chemICN^-(CO₂)_n show sharp contrast to trends previously observed in dihalide studies of \chemIBr^-(CO₂)_n and \chemI₂^-(CO₂)_n, but are strikingly similar to results found for \chemICl^-(CO₂)_n. Notably, a peak in the percentage of recombined photoproducts observed as a function of the number of solvent molecules shifts to larger n values as photon energy increases and does not reach 100% in the first solvation shell. It is likely that an intracluster reaction involving formation of the molecule \chemNCCO₂^- plays a significant role in the dynamics observed following excitation of the \chemICN^-(CO₂)_n anion.

Supported by NSF and AFOSR