NEUTRAL AND CATION SPECTROSCOPY OF FLUORENE-AR-N CLUSTERS

Fluorene-Ar-n complexes formed in a pulsed supersonic jet have been st udied in their S-1 state using two color REMPI spectroscopy with mass resolved detection. The appearance and shifts of the S-1 origins relat ive to the fluorene monomer are measured for cluster sizes up to n=30. The shifts and appearance of these bands are used to identify multipl e conformations at low n and have indicated a shift from two sided clu stering by Ar at low n to primarily one sided clustering at large n. T he ionic ground state of the smaller clusters (n less than or equal to 6) are studied using mass analyzed threshold ionization (MATI) spectr oscopy. The change of the ionization potentials as a function of clust er size has been determined. In the case of the fluorene-Ar-4 cluster, the MATI spectrum of two separate cluster conformations was measured, revealing significantly different ionization potentials. Vibrational dynamics has been studied in several smaller clusters (n less than or equal to 3) by measuring MATI and ZEKE spectra when pumping vibronic t ransitions in the fluorene chromophore. Significantly enhanced couplin g of the chromophore to van der Waals modes is observed in going from n=1 to n=3. (C) 1997 American Institute of Physics. [S0021-9606(97)031 44-9].