Generation of metal–ligand cluster ion beams through pulsed discharge ionization and ablation

Abstract

Pulsed capacitor discharge ionization in supersonic expansions was investigated for the production of intense beams of molecular cluster ions from seeded and ablated compounds. A pulsed discharge based on a triggered spark gap switch was designed and used as a method for ionization and ablation. Several combinations of nozzle geometry and electrode arrangement in front of a pulsed valve, were made to optimize the intensity of the ion beam as well as its composition. The cationic metal–ligand complexes Cu +–(methanol) n , Cu +–(acetone) n , Cu +–(toluene) n , Cu +–(water) n , and Al +–(water) n were synthesized by ablation of the metal from metallic discharge electrodes in a discharge gas mixture of helium seeded with the ligand of choice. The cluster mass spectra of the expanded plasmas show little background ion signal besides the metal–ligand species. Charge exchange processes in the expansion guarantee high ionization yields of the desired species and account for low backgrounds. Changes in the successive binding energy of Cu +–(water) n clusters n = 1–4 are clearly observed in the cluster mass spectra as step formation. A similar pattern found in Cu +–(acetone) n suggests the same trend in the successive binding energy as known for water.