Femtosecond photoelectron spectroscopy of I 2 2 „ CO 2 ... n clusters „ n 5 4 , 6 , 9 , 12 , 14 , 16 ...

The photodissociation dynamics of I2 ~CO2)n(n54 – 16) clusters excited at 780 nm have been studied with femtosecond photoelectron spectroscopy ~FPES!. The range of cluster sizes spans the uncaged and fully-caged product limits for this reaction. We observe time scales for a variety of processes in these clusters, including dissociation of the I2 2 chromophore, solvation of the I fragment, the onset of recombination on the ground state of I2 2 , vibrational relaxation, and solvent evaporation. In addition, substantial trapping in a ‘‘solvent-separated’’ state is seen for clusters with n>9; this state persists for at least 200 ps, the longest time delay probed here. Simulations of the spectra were performed in order to determine the time dependence of the electronic state populations, the I2 2 vibrational distribution, and the number of CO2 molecules in the cluster. Results are compared to previous experimental and theoretical studies of I2 ~CO2)n photodissociation, and to a recent FPES study of I2 ~Ar)n clusters. © 2000 American Institute of Physics. @S0021-9606~00!00102-1#