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

Pulsed capacitor discharge ionization in supersonic expansions was investig ated for the production of intense beams of molecular cluster ions from see ded and ablated compounds. A pulsed discharge based on a triggered spark ga p switch was designed and used as a method for ionization and ablation. Sev eral 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), we re 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 sig nal besides the metal-ligand species. Charge exchange processes in the expa nsion guarantee high ionization yields of the desired species and account f or low backgrounds. Changes in the successive binding energy of Cu+-(water) , clusters n = 1-4 are clearly observed in the cluster mass spectra as step formation. A similar pattern found in Cu+ -(acetone),, suggests the same t rend in the successive binding energy as known for water. (C) 2000 Elsevier Science B.V.