Photodissociation dynamics of IBr À „ CO 2 ... n , n Ë 15

We report the ionic photoproducts produced following photoexcitation of mass selected IBr(CO2)n , n50 – 14, cluster ions at 790 and 355 nm. These wavelengths provide single state excitation to two dissociative states, corresponding to the A8 P1/2 and B 2 S1/2 1 states of the IBr chromophore. Excitation of these states in IBr leads to production of I1Br and Br1I*, respectively. Potential energy curves for the six lowest electronic states of IBr are calculated, together with structures for IBr(CO2)n , n51 – 14. Translational energy release measurements on photodissociated IBr determine the I–Br bond strength to be 1.1060.04 eV; related measurements characterize the A8 P1/2←X S1/2 1 absorption band. Photodissociation product distributions are measured as a function of cluster size following excitation to the A8 P1/2 and B 2 S1/2 1 states. The solvent is shown to drive processes such as spin-orbit relaxation, charge transfer, recombination, and vibrational relaxation on the ground electronic state. Following excitation to the A8 P1/2 electronic state, IBr (CO2)n exhibits size-dependent cage fractions remarkably similar to those observed for I2 (CO2)n . In contrast, excitation to the B 2 S1/2 1 state shows extensive trapping in excited states that dominates the recombination behavior for all cluster sizes we investigated. Finally, a pump-probe experiment on IBr(CO2)8 determines the time required for recombination on the ground state following excitation to the A8 state. While the photofragmentation experiments establish 100% recombination in the ground electronic state for this and larger IBr cluster ions, the time required for recombination is found to be ;5 ns, some three orders of magnitude longer than observed for the analogous I2 2 cluster ion. Comparisons are made with similar experiments carried out on I2 (CO2)n and ICl (CO2)n cluster ions. © 2005 American Institute of Physics. @DOI: 10.1063/1.1839178#