Generation of "unstable" doubly charged metal ion complexes in a laser vaporization cluster source

Doubly charged metal ion complexes of the form M2+ (L)(n) are generated using a laser vaporization cluster source in conjunction with a time-of-flight mass spectrometer. Contrary to expectations, a variety of doubly charged species are produced with this source, including many so-called "unstable" or "metastable" ions in which the metal has a second ionization potential greater than the first ionization potential of the ligand or solvent. The species identified include Mg2+(CO2)(n), Mg2+(H2O), Mg2+(Ar)(n), Co2+(Ar)(n), Co2+(H2O), Si2+(Ar)(n) and Ti2+(CO2)(n). This is apparently the first observation by any means of Co2+(Ar)(n), Ti2+(CO2)(n) and Si2+(Ar)(n). Of the complexes studied, only the "stable" species Mg2+(Ar)(n) have been generated previously by laser vaporization. The conditions necessary for the production of these ions are investigated and possible mechanisms for their growth are suggested. Charge-transfer photodissociation is observed for. Co2+(Ar) complexes. (C) 2003 Elsevier Science B.V All rights reserved.