15min:

G. GREGOIRE, J. VELASQUEZ, M. A. DUNCAN, Department of Chemistry, University of Georgia, Athens, GA 30602, USA.

Mid-infrared (2100-2900 cm^-1) photodissociation spectra of mass selected Fe⁺-(CO₂)_n=2-6 clusters are presented. The observed fragmentation channels correspond to the loss of CO₂ molecules, their numbers depending on the infrared laser intensity. In low power condition, namely a few mJ/cm², clusters undergo simple evaporation of one CO₂ molecule, while at higher power (hundreds of mJ/cm²), multi photon absorption leads to multiple fragment detection, ranking from Fe⁺-(CO₂)_n-1 to Fe⁺-(CO₂)₂. In the latter case, step-by-step solvent evaporation within the temporal width of the laser (8ns) is observed, reflecting that the dissociation rate constant is faster than a few nanosecond. Photodissociation spectra of these clusters show a general blue shift of the resonant CO₂ asymmetric stretch within the complexes, and this shift decreases as the cluster size increases, which is consistent with the lowering of the Fe⁺-CO₂ interaction at the expense of the solvation. Furthermore, weaker transitions are observed which could correspond to combination bands with low frequency mode of about 20 cm^-1.