The electronic spectrum of cryogenic ruthenium-tris-bipyridine dications in vacuo.

We report the electronic spectrum of the prototypical ruthenium coordination complex Ru(bpy)3 (2+) (bpy = 2, 2'-bipyridine) by messenger tagging with N2 in a cryogenic ion trap and photodissociation spectroscopy of mass selected Ru(bpy)3 (2+) ⋅ N2 ions. We observe individual electronic bands and groups of bands with unprecedented detail, particularly in the usually unresolved metal-to-ligand charge transfer region of the spectrum. By comparing our experimental results with time-dependent density functional theory, both with and without spin-orbit interaction [Heully et al., J. Chem. Phys. 131, 184308 (2009)], we are able to assign the spectrum of the isolated ion.