Investigation of the Stabilities of Neutral and Ionic Lead and Lead-Antimony Clusters under Single and Multiphoton Ionization Conditions.

摘要

The fluence dependence of lead cluster ion distributions at 222 nanometers and 308 nanometers reveal markedly different behavior. Results obtained at 308 nanometers display a simple uniform increase in intensity with higher laser fluence with little change in relative intensities. At 222 nanometers, however, a significant transformation is found from a markedly different low fluence distribution to a high fluence pattern, which is essentially indistinguishable from that observed at 308 nanometers. It is concluded that mass spectra obtained at 308 nanometers, regardless of fluence, or at 222 nanometers and high fluence contain appreciable contributions from fragmentation. Hence, under these conditions, the mass spectra are found to be dominated by cluster ion stabilities. Magic numbers observed at both high and low fluence correspond well to those obtained using electron-impact ionization, and in many instances parallel the magic numbers characteristic of rare-gas clusters. This suggests the stabilities of both neutral and monovalent cationic lead clusters are largely determined by close-packing considerations, and are not appreciably influenced by electronic structure. Similar preferences for close-packed structures are also found for mixed-lead antimony clusters containing one or two antimony atoms that are ionized using fluence 308 nanometers excitation. Keywords: Ionic, Lead, Lead-antimony, Lasers, Multiphoton ionization, Reprints, Photophysics, Metal clusters. (jg)