Photoelectron spectroscopy of multiply charged anions.

Multiply charged anions (MCAs) are common in condensed phases but are challenging to study in the gas phase. An experimental technique, coupling photoelectron spectroscopy (PES) with electrospray ionization (ESI), has been developed to investigate the properties of free MCAs in the gas phase. This article reviews the principles of this technique and some initial findings about the intrinsic properties of MCAs. Examples include the observation of the repulsive Coulomb barrier that exists universally in MCAs and its effects on the dynamic stability and PES of MCAs. The solvation and solvent stabilization of MCAs have been studied in the gas phase and are also discussed. A second-generation low-temperature ESI-PES apparatus has been developed, which allows ion temperatures to be controlled from 10 to 350 K. New results from this low-temperature ESI-PES instrument are also reviewed, including doubly charged fullerene anions, inorganic metal complexes, and temperature-induced conformation changes of complex anions.