Novel Cationic Selenium-Cluster Nitride Species [SenN]+ (n=1-11) Formed by Laser Ablation of a Se Target in the Presence of N2

Abstract

Nitride cations of selenium clusters [SenN]+ (n = 1-11) were readily produced by laser ablation of a selenium disk that was surrounded by a trace amount of nitrogen seeded in helium and followed by supersonic expansion into a high vacuum. Even at high nitrogen partial pressures, the cluster mononitride cations were found to be essentially the only nitride products in the whole size range we studied. The exception was [Se3N2]+, which is known to be a stable five-membered ring with seven pi electrons. We propose that, in the laser-ablation plasma, the selenium clusters with n > 2 take on a chain conformation, and that the N species links the two ends of the selenium chains, thus forming stable mononitride cations of the cyclic selenium clusters. Their stability is supported by the results of ab initio calculations (at both B3LYP/ 6-31 + G* and MP2/6-31 + G* levels) and of mass-selected cluster-ion photodissociation experiments.