PHOTOELECTRON SPECTROSCOPIC STUDY OF CHARGE-TRANSFER STATES IN CLUSTERS

Excited charge transfer (CT) bands are observed in the photoelectron s pectra of mass-selected clusters consisting of halide anions (Cl-, Br- , I-) complexed with several different amine molecules. We attribute t hese bands to the detachment of electrons from the highest occupied mo lecular orbital of the amine ligands. We show that the vertical bindin g energies of the CT bands in the photoelectron spectra of the 1:1 com plexes are consistent with the results obtained from a simple electros tatic model. In clusters consisting of one chloride anion and several amine ligands, the relative intensity of the CT bands scales linearly with the number of ligands and reaches saturation at a given cluster s ize. The saturation size is 4 for the triethylamine ligand and larger than 8 for the smaller trimethylamine ligand. This size dependence is consistent with the observation of CT bands generated via direct ioniz ation of the nearest neighbors to the anion. We suggest that the size dependence of the observed CT bands could be used to evaluate the coor dination number of the solvated anions.