SPECTROSCOPY AND RELAXATION OF $I_{2}-Ar_{n}$ CLUSTERS: GEMINATE RECOMBINATION WITHIN SMALL GAS PHASE CLUSTERS.

Abstract

Small $I_{2}-Ar_{n}$ clusters were generated by supersonic expansion of $I_{2}$/Ar mixtures. Pulsed 193nm excitation was used to excite the ion-pair states of $I_{2}$ within the clusters. Upon excitation, the clusters emitted a broad band centered around 400nm. This feature was assigned to the $D^{\prime}-A^{\prime}$ transition of $I_{2}-Ar_{n}$. Interaction with the Ar ``cage” red-shifted the transition by more than 4000$cm^{-1}$ from the gas phase position. The metastability of $I_{2}(A^{\prime})$ within the clusters was demonstrated by using a pulsed dye laser to re-excite the $D^{\prime}-A^{\prime}$ transition. Intense LIF spectra were obtained $10\mu s$ after the 193nm pulse. 532nm excitation was used to photolyse $I_{2}$ within the clusters. $I_{2}(A^{\prime})$, formed by geminate recombination, was detected by laser excitation of the $D^{\prime}-A^{\prime}$ transition. Both clustered and free $I_{2}(A^{\prime})$ were observed. These results and qualitative models of the dynamical processes will be presented.