Vibrational relaxation in I2-(Ar)n (n=1,2,6,9) and I2-(CO2)n (n=1,4,5) clusters excited by femtosecond stimulated emission pumping

Vibrational relaxation dynamics in I-2(-)(Ar)(n) (n=1,2,6,9) and I-2(-)(CO2)(n) (n=1,4,5) clusters are studied using femtosecond stimulated emission pumping (fs-SEP) in conjunction with femtosecond photoelectron spectroscopy. fs-SEP generates coherently excited I-2(-) within the cluster; results are reported here for excitation energies of 0.57 and 0.75 eV. The time-dependent PE spectra track relaxation of the clustered I-2(-) through coherent intensity oscillations observed at short times (<10 ps) and shifts of the photoelectron spectra that can be seen out to several hundred picoseconds. The relaxation rates depend on the cluster type and excitation energy: the overall time scale in I-2(-)(CO2)(n) clusters is relatively independent of both, but in I-2(-)(Ar)(n) clusters the time scale generally increases with cluster size and decreases with excitation energy. The observed dynamics for I-2(-)(CO2) and several of the I-2(-)(Ar)(n) clusters directly probe the time scale for solvent evaporation. (C) 2003 American Institute of Physics.