Time-resolved studies of dynamics in molecular and cluster anions

Femtosecond photoelectron spectroscopy (FPES) is used to study the timeresolved photodissociation dynamics of clusters excited at I2~(CO2)n/4, 16 780 nm. The FPES experiment on shows that the I~ fragment I2~(CO2)4 formed by excitation to the repulsive state of initially pulls A@ 2%1@2, g I2~ away from the cluster, but by 0.2 ps it is drawn back to complex with more of the solvent molecules. In the n \ 16 cluster, where caging of the is I2~ known to be complete, FPES probes the recombination dynamics of the I2~ in considerable detail. SpeciÐcally, vibrational relaxation on the I2~ X 2&u` state and the accompanying evaporation on molecules can be followed 2 in real time. Vibrational relaxation is essentially complete by 10 ps, whereas solvent evaporation is not entirely complete by 200 ps. The spectra also show evidence for short-lived recombination on the state. The I2~ A 2%3@2, g results are compared to previous experimental results for clusters I2~(Ar)n and recent simulations of cluster dynamics.