We studied the anion clusters of anthracene, An(n)(-) (n=1-16), by mass spectrometry, photoelectron spectroscopy, and theoretical calculations. The magic numbers observed at n=5 and 13 indicated formation of the half-filled and completely-filled first solvation shell, respectively. We found that autodetachment could occur via a short-lived excited state of the anion, producing autodetached electrons at a nearly constant kinetic energy, irrespective of the photon energy. Three distinct forms of anion core previously proposed were confirmed that are monomeric, dimeric, and trimeric in nature. As the clusters grow in size from the monomer, the character of the anion core undergoes multiple switching until the first solvation shell is half-filled. Between the half-filled and completelyfilled first solvation shell, the coexistence of the monomeric and dimeric anion cores was observed at certain cluster sizes, most notably at n=8, 10, and 11. Only the monomeric form of anion core was observed once the first solvation shell is completely filled. (C) 2003 American Institute of Physics.
