Electronic photodissociation spectroscopy of isolated IrX62- (X=Cl,Br)

Photodissociation spectra of free doubly charged anions IrX62- (X=Cl,Br) were measured in the photon energy range from 1.5 to 2.9 eV. Both data sets show the same features as the spectra of the respective aqueous solutions. Compared to solution, the gas phase absorption bands of IrBr62- are redshifted by 0.01-0.15 eV. For IrCl62- no such shift could be observed. Photodissociation of IrBr62- results in the formation of Br-, IrBr4-, and IrBr5-. Fluence dependent measurements of fragment formation as well as parent ion depletion, allowed inferences regarding the dissociation pathway and the inner barrier height for the dissociation process which was estimated to be 1.6+/-0.2 eV. From measurements of the kinetic energy released upon fragmentation into monoanions, we estimate the outer barrier height to be 2.2+/-0.2 eV. (C) 2002 American Institute of Physics.