Electronic Spectra of Tris(2,2'-bipyridine)-M(II) Complex Ions in Vacuo (M = Fe and Os)

We measured the electronic spectra of mass-selected [M(bpy)₃]²⁺ (M = Fe and Os, bpy = 2,2'-bipyridine) ions in vacuo by photodissociation spectroscopy of their N₂ adducts, [M(bpy)₃]²⁺·N₂. Extensive band systems in the visible (predominantly charge transfer) and near-ultraviolet (ππ*) spectral regions are reported. The [M(bpy)₃]²⁺·N₂ target ions were prepared by condensing N₂ onto electrosprayed ions in a cryogenic ion trap at ca. 25 K and then mass-selected by time-of-flight mass spectrometry. The electronic photodissociation spectra of the cold, gas-phase ions closely reflect their intrinsic properties, i.e., without perturbation by solvent effects. The spectra are interpreted using time-dependent density functional theory calculations both with and without accounting for relativistic effects.