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

Abstract

Doubly charged metal ion complexes of the form M 2+(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 Mg 2+(CO 2) n , Mg 2+(H 2O), Mg 2+(Ar) n , Co 2+(Ar) n , Co 2+(H 2O), Si 2+(Ar) n and Ti 2+(CO 2) n . This is apparently the first observation by any means of Co 2+(Ar) n , Ti 2+(CO 2) n and Si 2+(Ar) n . Of the complexes studied, only the “stable” species Mg 2+(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 Co 2+(Ar) complexes.